I’m with Thea on this on, I always used American BC. I switched from American to SMBC and loving it. My biggest issue with American was sometimes when handling I would get a fold or bump in the cake where the cake and icing settled underneath the fondant and it changed shape. Didn’t always happen but when it did it was enough to ruin a good looking cake (at least to me). I know there are plenty of people that use it with no problems underneath their fondant. I am not one of those people, I can do it but not get the sharp edges I get with SMBC.
Cooking egg whites to 140F (60C) should be just fine. Salmonella starts dying off about 131F (55C) but I have taken it as high as 160F. Just make sure to properly store your icing and cakes!