I was sort of afraid to try SMBC and IMBC because there are so many posts about people having trouble. But I decided to try a batch of SMBC (because it seemed like the easier of the the two.) It worked fine for me, but I wasn't crazy about the taste. Then I made a lemon SMBC that used whole eggs - that was amazing! Then I made an SMBC with a couple whole eggs and the rest egg whites, plus extra vanilla. Again, amazing. Then I made a raspberry SMBC, using fresh raspberry puree... amazing. This week I made a caramel IMBC, again using part whole eggs, and used it to fill a Guiness chocolate cake. Wow!
I like it best when the cake is served at a temp below 75F, but I don't like it when it comes right out of the frig, either. Air conditioned house temp works good for me.
I'm finding both IMBC and SMBC to be easy to make and extremely forgiving. I like both best with strong flavors. This works really well for me as an alternative to refrigerated, perishable fillings... cream mousses, custards, etc. I do mostly fondant work and can't refrigerate a large cake. I use a layer of filling (no dam) that is about 3/8" thick.
I'll continue to use American (PS) buttercream for the cakes that I make for children, but from now on, I'm going with either IMBC or SMBC for my cakes made for adult crowds. The one exception is that I pair an all butter PS chocolate buttercream with chocolate ganache. I just can't give that one up yet