Choice of colours (body) and choice of emitter tint options too. Simply and effective UI. Compact and powerful, well built. I have at least 3 of them I use regularly.
To me the big plus would be a big deal. If I wanted to carry it in a holster (could pocket) I would be back to some kind of C8. A holster completely eliminates every advantage of the SC31 Pro that is my current co-EDC. (Go Ti3;-) When you add to that a single mode, eliminating moonlight, it is a no-brainer. Go for something with a C8 at least diameter reflector.
If the protected cell was simply a matter of safety, again going with the holster, I think the TN4-A would be the best choice. The Sofirn (4-AA) model as well due to its substantially lower price. I have pocketed the TN4A — way to big for my taste but doable. Haven’t used the holster that came with it but see no reason why it wouldn’t work as it should. Pretty much the same as a C8 except for the added weight of 4-AA vs 18650 (roughly same size reflector).