I feed it to two of mine. I picked it up in the feed shop, as I was only feeding a bit of chaff and the two where both in a decent amount of work. I just thought they could do with something extra ( both eventing) I know of one other horse on it, again in decent work ( eventing) , its the only thing he can have that doesn't make him go silly.
Currently using lo cal as she's lame and out of work but last summer I was doing endurance with my cob (about 40-50km per week training plus a couple of rides when I could get transport)
I really liked how she looked on it, and was generally very impressed.
I did have to top her up for energy levels - she was getting 1-2 mugfuls of the ease and excel depending on that weeks workload as I was finding about 2 hours into the ride she'd start flagging which dissapeared when she was started on the ease and excel alongside the performance balancer. This is her on the two together