Depends on the load of course, but in my experience having tied it a lot, it only jammed up once, taking an extra thirty seconds to undo. This was when I put about 200 lb on it and swung around a bunch. Jute rope also has a ton of friction, synthetic being smoother would be even less likely to jam.
It's an interesting and decorative knot - I've not seen anything like it before. I'll have to give it a try. I'm trying to think of another quality bight knot that can be tied with the object in place. Not the bowline, not the butterfly.
If you want another one, check out the WykD Fast Bowline. It can be tied as both a regular version and a quick release. It is even simpler but has less symmetry. Interestingly, the quick release is more structurally sound with this one. There is also a variant of the Somerville where the loop is made backwards, which seems to go by Struggler’s knot. It purports to be nearly as strong, and supposedly can be tied with one hand.
Also, there is a method of tying the Somerville called the reverse Somerville. It’s the same knot but tied inline rather than with the bight.
The downside to the Somerville is that you generally can’t get it really tight around the object. A variant of it exists which allows you to do so at the cost of a bulkier knot: before making the loop, cross the bight over all the rope, go under it and come back to where it just was, similar to how you would start a reef knot. I have used that technique before with some success but not enough to recommend it beyond messing around.
