Just to update, I got my EWK M&P .22 Compact thread adapter today, so thanks to EWK for getting it out to me so speedily.
It's interesting to compare my Gemtech .22 (full size) thread adapter to this EWK.
The only major difference is of course the way you tighten the adapter to the barrel. If fouling doesn't become a major issue (which it really shouldn't if you clean your guns even reasonably often), then I think the internal EWK method is potentially less... hazardous to your gun..
I don't know about anyone else, but I get very nervous using the wrench tool that comes with my S&W M&P .22 (full size) when I tighten/untighten either the factory thread protector or tighten/untighten the Gemtech thread adapter. One slip of the wrench and I know I'm going to gouge either the easily-marred aluminum slide or the polymer frame. I know because I've almost done it a couple of times... I don't see either of those things happening with the EWK. Frankly, the allen-key design makes too much sense to me! Time will tell if fouling becomes an issue. If it doesn't, I'd take this EWK design any day of the week over the wrench design.
Either way, let's face it, it's just a thread with a cover, so any of them should do the job. I will say, it would have been nice for an extra dollar or two to see an option of a 1/4" allen key in the package. I don't have a dedicated 1/4" allen key, since I just have a set of allen keys, and I'd like to have a dedicated one for the range bag. Not a biggie, though.
Overall, though, the EWK seems great value for money when you factor in the pricing elsewhere. The thread protector looks high quality, - it screws on easily and smoothly. The idea of spending $68 (which is over 20% of the price of the M&P .22 compact itself - and about 25% of the price some people have been getting the compact for!) is just... sinful. So it's good to see EWK take on a more conservative (read: realistic) approach here.
The only thing I'm missing now is my M&P .22 Compact.

Hopefully this week I'll get to pick one up and actually use my new Specter II!