I have both the UCD 60 with a Saito 100 and the Mayhem with a YS 110. I really like both planes and think the fun factor is great on both. But I like my Mayhem the best. It doesn't give up anything to the UCD and I think it flys more precise. It knife edges a lot better, flat spins are a little flatter and does the waterfalls tighter. No putting down the UCD as I have both 46 and 60, I just think the Mayhem is better. Some of my feelings may be based on the YS Engine which allows CG placement of fuel tank and has a little more power, but I'm trying to limit opinion based on flying capabilities only.
Thanks,
Barry