I have now done a few trades and played around with their API. Average execution-speed for me was ca. 950ms (altho, i ping around 200ms to their servers).
Spreads are good, the "inversed" quotes during fast markets dont seem to be a big problem for me. I think its hard to exploit them, the price might be anywhere after around 1 second execution speed. Maybe its possible with a really fast connection to them and an api-application..
Their api is pretty neat. Its done with COM-objects, you can hack something up pretty fast if you are familiar with a com-compliant language. Beats IBs java-thing in my opinion. They dont provide backfill-data tho, which makes things complicated if you need them. Esignal has their data in the GTIS feed ("3DFX").
In a FX account you can only trade FX, and no futures, stocks, etc. I think that sucks.
Commissions are well, 50/mio. In the end, its comparable with other retail-plattforms like oanda. They dont have a dent on more professional multibank-plattforms with $50, but i think its ok for the retail-sector. They have a hard time competing with IB tho, IMO.