A 0.1 pip mark-up is added to spread for the use of MT4.
That quote from FXCM appears on
this page. Unsure if it only applies to FXCM-US accounts, but I would definitely ask if you're considering an MT4 account.
Regarding the multi-session authorization... I personally don't see what the big deal is? I know FXCM has different jurisdictions, and perhaps yours requires this legal hoop. Even if you had 10 or more accounts, it doesn't seem to be that big of a problem. You only need the authorization once per new account opened.