I asked the same question a few months back
I was getting a few emails from them, however never got replies, and with no other contact details other than their username@gargurus email address its impossible to track them down. I'd send 4/5 emails at different times of the day and was getting no replies at all.
I did my months free trial ( i think they charge £250 per month to be a full member ) and got very little from it at all too so was not impressed.
HOWEVER - in the last few weeks I have had 4/5 enquires and have dealt 3 of them! Quick replies and deals done pretty much the same day - but all from a distance away ( Birmingham/Newark/Scotland )
Had one this morning too, but no reply yet.
I'm not prepared to pay £250 a month for it, and am quite happy to reply to the leads and see what happens. They try to sell the marketing and analytics bit of it, however You can sit and look at stats all day autotrader/gumtree/ebay/google and still be non the wiser...
I'm on the cheap side of the fence ( well the free side! )
Mat