Nice job. I agree with pretty much everything you wrote. A few comments ...
Bolden looks physical, strong, willful runner. Competed well with Ridley and Vereen for snaps, and earned a spot on the roster. You wonder how he went undrafted.
Bolden is a big, physical runner (like BJGE before him at Mississippi St.) who has more explosiveness and better receiving ability. He was injured his senior year which affected his draft stock. There was competition for him as a UDFA, and he showed enough in preseason to make it likely that he wouldn't clear waivers and to justify a spot.
McDonald stands out because he can play all five OL positions. In preseason games, he was at OC one series and RT the next. Pretty incredible. Not overwhelming at any position, but improving, and has the mental side of it down. Bottom line, he creates incredible roster versatility which BB loves.
Exactly. McDonald is Mr. Versatility on the OL, and BB loves those guys. He has a high football IQ, understands the different dimensions of line play, and is young enough to still have a lot of upside. He started 2 games at center last year and played decently, and has received praise from other Pats OL vets and from BB.
Thomas can play OC and OG. At center, he looked better than Koppen, and looked good at OG pulling in the run game. Has the skills to be our starting RG, if Waters does not report. But more likely playing behind Waters, Connolly and Wendell... which is a nice, deep depth chart.
Thomas was one of the surprises of the OL during training camp, and consistently outplayed other guys. That, combined with youth and versatility, earned him a spot.
Fortson showed some interior pass rush. He's one that occasionally looked explosive in camp, but I think he's a project. Guess he looked too good to risk on waivers?
Forston is a penetrating DT with a lot of upside who was injured a lot in college. He was once projected as a possible high draft pick. I thought he could be viewed as a long term replacement for Myron Pryor as an interior sub rusher, and with Pryor on PUP and Forston showing some flashes it makes sense to give him a chance. It would be easier to sneak him onto the PS after week 6 if Pryor comes back.
Francis sparked in camp, too, enough to push Gerard Warren off the roster. I think he's another one where BB saw value for the salary. And I think he likes bringing hard working, coachable UDFAs onto his roster whenever they flash something in camp. I think Francis is depth behind Brace, and his 2013 replacement.
Francis was a big surprise, and shows the ability to play both inside and out. Another young guy with a high motor and a lot of versatility.
Rivera is the primary beneficiary of the Dane Fletcher injury, but that said, he earned the job against quality competition. He matched Tarpinian and Koutoutvides on ST, and outperformed them at ILB in the regular defense. He was the guy calling plays for the 2nd team D. Looked reliable, made plays against the run.
Rivera was the biggest surprise for me. I had Jeff Tarpinian slotted for his spot, but BB apparently thought that Rivera outplayed Tarp. That's ok by me. I'd rather have Dane Fletcher, but that won't happen this year.
A couple of these guys could easily be headed for the PS at some point this year, but they showed enough that it would have been dicey to expose them to waivers at this time. As last year showed, other teams are eager to snap up BB's leftovers. Making such moves during the season is often easier, as teams are looking more for experienced vets who can contribute immediately.