An extremely fun mod and a good way of bringing Mecha Mark.1 and Silver Sonic into SRB2!
Silver Sonic is the less absurdly powerful of the two characters here, but he's absurdly fun to control considering he bounces everywhere and gets fun movement options, especially his Air-Spindash. Probably one of my favorite characters to play as in this game.
Mecha Sonic is also very good, a fairly overpowered beast with some unique restrictions, such as having a spindash but still being too big to fit into small gaps, similar to Espio. However, despite his impressive kit, he has one major issue that brings him down and leaves me rating 4 stars instead of 5: a gamebreaking bug which makes the campaign unwinnable.
Y'see, Mecha has a unique part of his kit that triggers upon entering a level where a shockwave obliterates any enemies around him upon spawning. This does proves useful, making it so bosses only have to get seven times instead of eight, and it even removes the cage on CEZ3, turning the boss into kind of a joke. However, this quickly becomes a huge issue in ACZ3. This shockwave damages Fang before he actually gets to exit the box in the beginning, starting the fight earlier than it's supposed to. The result of this is that Fang is invincible. I actually don't know how this is in the game, since the trailer clearly seems to imply testing against Fang was done, so it's somehow just me getting this, or the testers just didn't fight Fang and assumed everything was working well.
Still, this is a really good set of characters to mess around with! Just maybe don't play story mode with Mecha for a while until a new version comes out.