Dedicated lowers all the way and don't look back. Take it from a guy that have done both. Mag block conversion is not worth the time, effort, or money. Sure they may work fine, but I guarantee you'll be fiddling/adjusting the mag block to get it to run 100%. Yeah its no big deal to adjust the block, but you'll need tools, which you may not have or forgot to bring while you're at the range. I went through 2 different mag blocks before finding one that worked perfectly (Hanh). Back then dedicated lowers did not exist and mag blocks were the only options. I had even considered pining the block to the lower (like Colt's 9mm) as it was the only way to ensure it would not move. When DDLES came out with their dedicated lowers I went through the same debate you are. Once I bought the DDLES lower I never regretted it. My 9mm now runs 100% all the time. This is how the 9mm AR should look and run from the very beginning. No more lingering doubts about mag block issue again. If I could make a personal suggestion, buy the Quarter Circle 10 or Black Creek Precision lowers. Stay away from the CMMG and Rock River Arms. Nothing wrong with them and I sure they run fine, its that they look just like your standard AR lowers.