I have the original sE Reflexion Filter (now called the Reflexion Filter Pro since they released their cheaper home studio models). I find it excellent--properly set up it frankly sounds darn near as good as a professionally treated studio. However, the "properly set up" in that sentence is the key phrase. You really have to follow the sE instructions to the letter and it's a game where millimetres make a difference. Also, you need a good, heavy duty stand--the beast is pretty heavy. My use is mainly for the spoken word--I've not found the need for it very often for singing (though I have used it from time to time).
I've also tried the Project Studio Baby Reflexion Filter, although I don't own one. It was darn good though not quite in the same league as its big brother. Talking to another user, we came up with the phrase "80% as good for 50% of the price".
Besides the need for a good mic stand, the only other down side of either of these is the difficulty of finding a place to put music, scripts, etc. (which is important for voice recording). I notice that sE is selling some kind of clamp-on music stand now but I've not seen it or tried it.