I tried two Ignition Club basses in one of my local shops, about a year and half ago. I also am a Rumblekat owner. Here's my impressions:
1. Rumblekat has much better pickups. When I tried the Club Ignitions in the store, I played them through the same amp that I use at home (they just happened to have one in the store), and the Clubs were anemic. Lower output, thinner sound; the Rumblekat absolutely rumbles by comparison.
2. The build quality on Rumblekat also is better. When I worked those little switches on the Club Ignitions (the "solo" and "rhythm" switches, I think they're called), the switches felt like they were going to break. Maybe they wouldn't have, but they felt flimsy.
3. The Rumblekat also felt more solid to me. This probably relates to weight -- the Club Ignitions were light as a feather compared to the Rumblekat. That's the only plus the Club Ignitions had for me.
I went to that store because I wanted to try, and hopefully buy, a Club Ignition, but that experience changed my mind about them.
Of course, others may have a very different opinion.