YS engines are great.

The stock engine mount is a little soft (IMHO) for the YS, but otherwise works just fine (I have a Saito 100, a friend a YS91 and another friend had a YS120 in the Excellerons).

The control horns on my plane have worked great so far after many many flights, but the ones in my friends plane have been breaking since the beginning, so far 2 broken and 1 cracked (all in the elevator). When he was assembling his plane I noted the base of his horns was a lot flimsier(sp?) than mine, you can easily bend the plastic holding the screw with a finger with little effort (as opposed top mine). But I don't know how prevalent this problem is.
What I would suggest is to do whatever makes you feel secure, if they look flimsy to you, change them, why risk the plane?

Best regards,

Gabriel