I used a pair of those modular dropouts on my MTB and the bolt on dropouts have not been a problem, except for some rusting of the bolts. The main downside of using those dropouts is disc brake mounting. Using an IS tab is very difficult, because the tab hangs off the back of the frame component in the seatstay orientation. It can be mounted on the chainstay, but the seatstay must be bent to allow clearance for the brake caliper. They may work OK with Post Mount or Flat Mount, but I haven't tried either of those with the modular dropouts. I have pics of two frames that I used them on with chainstay IS tabs, if anyone needs to see what I'm talking about.