Swamptrout I use a JG for low and slow, I was going to get a slow and sear for the same purpose but the cost of the SnS put me off. The JG is mild steel (S&S stainless) so despite seasoning it, it has gone pretty gross. I could sand and re-season but it doesn't bother me.
I love using this setup for L&S , and yes water tray with boiling water under the grill and it ticks away for a long time. You can get an easy 8 or 9 hours without dropping temps at say 135degC, and you can get longer with running a lower temp or if you "overload" with briquettes so your grill flap sits on an angle you'll get a few more hours too. You could get "longer" with a snake, but I just love the convenience of lighting 20 beads, dumping them in a corner then filling the rest with unlit. You do need to pay attention when pre-heating, stopping down the vents as you go to hit your setpoint and settle the temps works best. If you go over it can get away from you as there is a bucket load of charcoal begging for a burning. This highlights an advantage over snake on cold/windy days where a snake can struggle to get over 100C as there is only so much charcoal that can be lit really but the JG (or S&S) you just have to give it more air and it will burn more of the minioned pile off.
Also, this setup makes it very, very easy to reload charcoal and add more smoking chunks too.
I've never actually used it, or the kettle for that matter, for the "sear" part of a reverse sear. I've only ever just cranked the gasser at this point instead of trying to time when I needed to get another chimney cranking to reload etc. I'm not convinced searing over charcoal compared to gas will give you any flavour anyway (particularly after a dedicated smoke phase). Either of these side loaders work great for low and slow, but honestly I wouldn't bother getting them to do a reverse sear myself.