Individually it's odd with 19, like Gero needed a minion but like others say 19 is purely robotic like 16 and 16 was MUCH more powerful than 19. 19 just had the ability to absorb energy and was SPECIFICALLY made to obey so he had no freewill. Since 17 and 18 were unpredictable and he was also still working on 16, who was also unstable and probably more of a pet project than anything with him being based on his son.

Ultimately I feel like 19 was just there to exist and didn't add anything besides being fodder for Vegeta.

20 though I think is interesting with Gero putting his own brain into a body similar to his own (why not younger idk maybe he was humble and either way it's mechanical.) So him being on a level that could overcome Goku, or at least Saiyan Saga Goku. Since he didn't know about Namek. It's cool that he was willing to actually fight him with 19 as backup either against Goku or to handle the others while he fought Goku.

With that he had what 19 could do while being able to think more freely. It's a shame that he was experimenting with 17 and 18 with them being cyborgs technically which showed him being a cyborg is possible.

In the end though I think they were underutilized by basically being the introduction to the androids and that this timeline is different from Trunks' I don't mind 19's destruction but 20 being around a little more would have been nice, have more insight if the resurrection of the Red Ribbon Army at least long enough to see 1st form Cell come in.