Despite the price (unless i can find one cheap on ebay), I'm seriously considering the Sprinco. Not for its recoil reducing claims, but because it's metal.
Some -- including myself -- are wary of putting aftermarket accessories on their gun. Especially accessories that could effect reliability, which is paramount in a defensive handgun.
That said, it's been my experience that the plastic recoil guide rod is inherently unreliable. To be more specific it breaks in half, rendering the handgun useless.
If you'd like to see for yourself, search for my post from ~2 months ago. As part of routine maintenance, I ordered a replacement guide rod from S&W. My original guide rod was working fine, but the spring had seen it's more than it's share of use after 4 years of ownership and many trips to the range.
In short, my "new" guide rod broke (snapped in half) after only a couple of months. There's a pic of said guide rod in my post.
My P99 now has the original installed, but my confidence in either 1) the design or 2) the Q/C is very shaken.
I don't believe for a moment these PR statements about it acting as a "cooling fan" for the barrel. It's just cheaper to produce. Of course they can't say as much, but they have to put a positive spin on it.
S&W cust. service has been surprisingly responsive, but it's been a long time, and I still have not rec'd a replacement. Apparently, the expected shipment hasn't arrived from Germany.
For those that have the sprinco, how many rounds (approx.) have you put downrange? If the number is high enough and reliability 100%, I may purchase one.
And for the record, the plastic guide rod is the only "weak link" in the P99. I've owned handguns that were 99.9% reliability wise. The P99 has been 100% since day one. It's the only handgun that I'd fully entrust my own and my families life to.