Handling wise they're not too dissimilar – my Soda has shorter forks/longer stem/narrower bars than the BFe, so they're about the same speed and balance in steering. The Bfe is obviously a lot shorter, and that's really noticeable on stupid steep tight stuff – the Soda is still manageable, but needs more care. The BFe also manuals like a dream, but that then comes and bites you when you try and ride it *up* something proper steep (although it's surprisingly OK uphill).
Ride? Well the BFe is a LOT more direct. I wouldn't call it harsh, but it's definitely way more solid than the Soda. It probably is stiffer under power, but a) I'm a skinny bugger so don't generate a lot of power and b) the bike is a lot heavier and has bigger, heavier tyres and wheels. Its certainly not a bike I'd fancy doing a 6 or 8 hour XC ride on, sat down most of the way, but for playing about in the woods in a grind up, thrash down kinda way, it's magic.
As far as flexibility goes – having watched what Robbie Rickman has been getting up to on his Simple, I don't think us mere mortals ever need to worry about whether a Soul is strong enough. Although if we can persuade Cy to make a Ti Bfe, then I could combine 2 bikes into one….