Given that there are several measurements around for the Mad Dog, Paradox, and even the DIY BMF mods, I would feel much safer going with a known/proven great product until we can get some more objectivity around this particular mod. I don't really trust random T50RP mods anymore because you can really mess them up, and the amount of research and QC behind the Mad Dog or Paradox are pretty darn good. Plus, at that price, you might as well just go the DIY route and save that extra last bit of cash. The guy is probably doing nothing that hasn't already been publicly discussed.
Plus MrSpeakers has a full blown business behind this, so I'd imagine he would be able to offer better customer service. Also, his custom pads are the best I've used on the T50RP yet, and he's got the sound nailed down. Each unit is tested to make sure it meets the sound specs, as there is variation between individually T50RP units (verified by both MrSpeakers/Dan, LFF, purrin, etc.).
If you're going to go with a less proven route, just save the cash and DIY. Otherwise I'd stick with the Mad Dog (I never had luck getting my T50RP mods to sound as good as the MD).
That's just my opinion, though, and I could be entirely wrong about this ZMF mod. I have become highly wary of most subjective impressions over the years, and audio stuff isn't cheap. I try to make safe purchases with objective and subjective impressions (from people I trust) to lessen the risk of purchasing a product I end up not liking, even if this costs me more in the end.