I'm on R2 (I assume their second failover server). I know for a fact that there was an issue on R1 (probably the 1st failover server). Generally, the "proof of concept" will probably take some time.
Unless there's a failure on one of the 2 machines running R2, I won't be able to tell you how effective the implementation of the concept is.
I've been using them for over a year (1 Advanced-One, 1 Budget-One, 1 Failover-One) and I'm very happy with ResellerZoom. I've had issues with them but they've always been very responsive, helpful, and courteous.
What I like is that their forum is open, honest, and well-moderated. You see both the good and the bad.
Right now, it's too early too tell how Failover will perform. You may want to check back again in about 3 months.