I've used this biner a decent amount as a belay biner, primarily with a GriGri 2, and it does its job quite well. The spur totally captures the belay loop, and the magnetron locking system is reliable, quick, and easy to use.
When using this product with a GriGri, the manual recommends capturing the belay device with the spur and leaving the belay loop in the larger opening. This does result in an extra step or two when attempting to take your partner off belay, which is a tad fumbly and obnoxious. I also feel way more likely to drop my Grigri, and probably would not take this multipitching.
I recognize that these are setbacks of the Gridlock, and not the Magnetron locking system, which I like quite a bit despite its added weight.
Also obnoxious about the gridlock is the way that it hangs awkwardly from a gear loop. Blech.
All in all, the Magnetron is super nifty, and works really well, and the Gridlock has its place. This would be a great 2nd belay biner especially safe and foolproof for sport climbing, but I'll keep using a vaporlock or attache screwlock for multipitch.