FWIW, these bets are fairly straightforward to price and are traded upwards of $100MM notional per ticket in the OTC markets. Standard deals are monthly out to five years, so the short-duration bets are pure stat-vol and difficult for IG to hedge. IOW, they're not overtly trying to rape you...
I've traded on IG for a year or so, but not currently. The daily Euro-convention binaries have been 4-wide during the time I've traded. You're stating that there are 8-wide markets on the major-FX binaries?
Regarding betsfortraders.com.... a friend of mine in the EU has been very profitable, but has yet to receive his requested withdrawal, [between 5-10k Euro]. He submitted the withdrawal over two weeks ago.
I would not deposit a dime with betsfortraders.com