Mipro has been around for quite a while and while maybe not as well known not Shure, Sennheiser, Audio-Technica or even Lectrosonics, Mipro is hardly an unknown brand nor is it another 'cheap wireless', in fact they used to OEM the wireless products for some well known brand names. I also believe that Mipro was the first to use IR programming between the transmitter and receiver.
I've used Mipro for some schools without any problems and there seem to be quite a few positive reviews out there. And while they may not compete with some of the better known, higher end products, I also know how Ray Rayburn is about what he offers and don't think that he'd be selling them Mipro if they did not represent an acceptable level of quality and value. So I think the product itself is worth considering.
What may be more important is your situation. If you already offer other brands, would Mipro let you offer better quality gear for a similar price or similar gear for a lower price? Might it affect meeting minimum sales or special pricing or anything like that for your existing brands? How comfortable are you with the technical and service support offered?