Vertically split rings are not necessarily bad. There certainly can be bad rings that happen to be vertically split, but it's not absolutely because they are vertically split (i.e. - getting quality made rings is of first and foremost importance). In our experience, though, it would be incorrect to say that vertically split rings are no different that horizontally split rings. Generally speaking, with horizontally split rings you simply level the scope in the bottom half, begin to torque down the top half while maintaining level, torque using a torque wrench in an alternating fashion like you'd do lug nuts on a wheel and you're done.

Their vertically split counterparts, however, need to be tightened a bit differently. Rather than tightening in an alternating pattern and going for an "Even ring gap" where the gaps between the two halves on either side are evenly spaced, you actually want to close one of the sides completely prior to even beginning to tighten the other side. Take our Pro rings for example - a fine ring made by Warne who is well known for producing quality rings. There's nothing wrong with them, but we've seen issues when people try to tighten them like a horizontal ring - even at proper torque spec, the scope slips or there is an impingement on the tube that causes issues with zeroing or tracking. In nearly all these cases, simply un-mounting the optic and re-mounting, torquing the top two screws on each ring down *first* to 18 inch pounds before even beginning to tighten the bottom screws, then moving to the bottoms to torque to 16 inch pounds solves to problem completely. On our ADM mounts of old which were vertically split, it was the bottom two that needed to be torqued first, and this also caused a number of issues for people who were tightening improperly (Hence the reason we switched to horizontally split in the newest and most current version)

And as a few others have noted, don't use loc-tite on the screws that clamp the rings around the scope tube on any type of ring - it will lubricate the threads and your torque wrench will cam over at what it "Thinks" is 16-18 inch pounds, for example, but really the screws have tightened as much as 20% beyond that, which, depending on the application, could begin to cause issues with any scope. We've been mounting and using scopes with rings torqued with zero loc-tite for years in the harshest conditions on the harshest of rifles without any issue whatsoever. If that weren't the case, we wouldn't still be recommending against it to this day.

In short - Vertically split rings can be fine, just don't try to tighten them like a horizontally split ring.