OK, I'll add my two cents to the confusion. In the spirit of full disclosure, I also just bought a Remington 870 and am looking for good ghostring sights.
Price$: Trak-lock comes out ahead here at $140 with tritium, $115 without. MMC is next, with prices ranging from $133 for the lowest cost, no-tritium option, to $188 for the priciest tritium combos. Precision comes in at $170 and $230, without and with tritium, respectively.
Tritium: All three offer it, and they all have different interpretations. From the descriptions on the web sites, it looks like the Trak-lock sights only have the tritium on the front, with nothing on the rear. (Can anyone out there confirm this?) MMC offers a tritium dot front with a tritium bar at the bottom of the ring on the rear. Precision offers a tritium dot front with, from my interpretation of the description (someone who actually has a set, feel free to correct me) two dots in the rear, making it like a three-dot pistol sight when used in the dark. Also looking at Precision's description, which says "Includes replacement Tritium front and rear sight inserts", it would seem that you have to install the things yourself, or have your smith do it. From my experience with pistols, I personnally prefer the three dot set-up at being the quickest and easiest to acquire and line up.
Other stuff: from the pictures, the Trak-loks lack the "ears" on the sides to protect the rear sight that the other two have. However, the Trak-lok looks like it's lower profile and less likely to get snagged that the other two. From everything I've read, the folks at Wilson Combat generally know what they're doing when it comes to guns.
All that being said, I'm inclined to go with the Precision sights, despite the higher cost. The deciding factor for me right now is the 3-dot tritiums, which just work better for me.