They're OP in the sense that you can put high tier parts on them due to the low cost. They're not OP in the sense that the times you need to hit on several courses require proper play and a mix of parts is better than all the best (Courses 3 and 7 if I remember right don't even use the high tier stuff, they use stuff that boost acceleration). I would argue they're not worth it in any way even if you're willing to burn your money. Plus, you can just buy the highest tier stuff and make them anyway and look at a guide for optimal parts, you only need like four million yen or so for that.
Majima Everywhere is annoying as sin even though the actual content isn't that bad and you can't turn it off, DoD is destroyed despite being Kiryu's main style (The person who thought needing Heat for Double Finishers deserves a slap upside the head), Kiwami healing for bosses is obnoxious, enemies knock you down at the slightest breeze (Though Kenzan's mooks stabbing you have them beat), and there's only like two bosses that actually have their original moveset or improvements to it, the rest just take bosses from various games (Specifically 3, 5, Ishin, and 0). It's not terrible but there's some bad decisions made in a lot of places.
