The Mets bringing Sean Manaea on board might not be a Yoshinobu Yamamoto-sized splash, but he could definitely be a valuable addition to their pitching staff.

Manaea made some interesting adjustments to his repertoire with the Giants last season that will be worth watching in 2024. He added several mph to his fastball velocity after training at Driveline in the offseason. He started throwing a sweeper, the trendy new type of slider that's becoming increasingly popular in MLB. And he improved his changeup, a necessary third pitch if the Mets want to use him as a starter.

The key question is, which of those changes will the left-hander carry with him to New York?

Here are the three factors that will determine whether the Mets can get the best version of Manaea next season.

• The hot new pitch that's sweeping across the Majors

1) Will he embrace the sweeper?

Since reports came out of Manaea's agreement with the Mets, there's been a lot of talk about how his new sweeper was a key to his success in 2023, and could continue to be in 2024. And that's generally true. But there's more to it.

Yes, Manaea did add a sweeper last May that helped spark his success when the Giants moved him to the bullpen. He stopped throwing his old slider -- a traditional one, thrown harder with tighter movement -- and started throwing the "sweeper" style of slider that comes in slower but with a lot of horizontal break.

And Manaea's sweeper was, in fact, a good pitch. It averaged 12 inches of break, compared to the 2 inches he averaged on his old slider. He held hitters to a .140 batting average against the sweeper, compared to .284 against his regular slider. And he generated a 35% swing-and-miss rate, compared to 26% with his slider.

But here's the thing: Manaea only threw his sweeper as a reliever. In the two months San Francisco used him as a starter -- April, before he added the sweeper to his pitch mix, and September, when the Giants moved him back into the rotation -- he only threw his normal slider.

Here's Manaea's slider vs. sweeper usage over the course of the 2023 season:

After introducing the sweeper, Manaea worked it into his repertoire more and more, until he was throwing it a season-high 25% of the time in August, compared to just 4% sliders. But when he became a starter again, the sweeper was gone and the slider was back.

So if the Mets want Manaea as a starting pitcher in 2024, will he throw the sweeper? It's an important question. His harder slider can still be effective, but his sweeper sure looks like it might be the better pitch, if his successful results from last year can inspire him to keep it a focal point of his arsenal.

Manaea's sweeper also seems like it would pair well with his four-seamer and changeup, which break similar amounts but in the opposite direction -- while his sweeper breaks 12 inches from left to right, his four-seamer runs 15 inches and his changeup fades 13 inches right to left. At the least, the sweeper is a pitch Manaea should probably be throwing in tandem with his slider, no matter his role.

2) Can he maintain his velo bump? 

The big difference that jumped out about Manaea from the start last season, even before the sweeper came into play, was his velocity. He was throwing significantly harder than he ever had.

Manaea averaged 94.3 mph on his fastball in April, three full mph faster than the 91.3 mph he averaged in 2022 with the Padres. He maintained the bulk of those gains throughout the season, and even though he dipped a little bit when he went back to the rotation in September -- which is normal, since relievers can put extra juice into shorter outings -- he was still throwing over a tick-and-a-half faster (92.9 mph) than the year before.

That seems to indicate Manaea's velocity gain is for real, a good sign for the Mets. Overall, his 93.6 mph fastball velocity in 2023, at age 31, was the highest of his career.

That added velo, coupled with the good running action Manaea gets on his four-seamer -- his 15 inches of run gave him top-five movement above average -- made his heater a better pitch than it's been in a long time. Manaea's four-seamer was worth +6 runs prevented for the Giants, the highest run value for his primary fastball in a season since 2019. In 2022, his four-seamer had a -3 run value.

3) Is his changeup for real?

Manaea relies on his changeup to attack right-handed hitters no matter if he's in the starting rotation or the bullpen, but it's especially important for him as a third pitch as a starter. His highest changeup usage last season came in April (23%) and September (24%), while it had taken a back seat to his sweeper when he was pitching in relief.

That means the Mets should be looking for Manaea to keep up his changeup usage if he's in their rotation. The positive there is that his changeup was much improved last season. Manaea produced a +4 run value on that offering in 2023, solidly above average, compared to a -10 run value in 2022, when it was one of the worst changeups in baseball.

What made it improve so much? At first, it seemed like a better velocity differential with his fastball was the driving cause. With Manaea's fastball sitting at 94.3 mph in April, and his changeup at 85.8 mph, the difference between the two pitches was 8.5 mph; in 2022, Manaea's fastball-changeup velocity differential was just 6.4 mph.

But at the end of the season, his changeup was still good, even though the velo differential was much smaller (only 5.8 mph in September, with his four-seamer sitting at 92.9 mph and his changeup at 87.1 mph).

The key down the stretch seems to be that Manaea kept inducing strong drop on his changeup even when he was throwing it harder. Looking at 2022, for example, Manaea's changeup averaged 84.9 mph with 31 inches of drop. In 2023, at a much higher average velo of 86.6 mph, his changeup still averaged those same 31 inches of drop. That took his changeup from below-average drop to above-average drop.

Manaea's 2023 season makes him look like a pitcher who's still evolving. If he continues what he started, and rolls everything together going into 2024, the Mets will have found a bargain.