I've been running my HA 2.1 now for almost six years now as my daily driver, with no problems whatsoever, and can answer some questions, here.
The 2.1 originally came with the low flow pump, but that was replaced with the medium flow option in response to the times they took to fill a bag. The low flow pump takes a couple of minutes, whereas the medium flow pump takes around a minute, iirc. I prefer the low flow pump myself, since it adds less air to the bag overall, giving a higher vapour-to-air ratio. There is also a high flow pump to use with the 3 or 5 way mouthpiece, to make many bags at once, which is great for groups, or demos.
The 2.2 included changes to the newer pump, as well as a different LED lighting indication. It also included upgraded electronics connection types on the inside. Both the 2.1 and 2.2 have the 30 minute auto shutoffs included. The reason that they go to ~ 400F only is to make it impossible to combust.
As far as a valve, I found that after the first hit, the inside bag pressure more or less equalizes to ambient pressure, and leakage is not a factor at this point, imo. For times where you want to space out your bag sessions, I use a simple cap, as shown below. Keep in mind that you don't want to take too long when hitting the bags, as the vapour will oxidize, and become stale (lose taste) after ~ 30 minutes or so.
A couple of tips for the new users:
First, always keep the mouthpiece in the unit as it heats and cools as this will ensure that it seals much better, long term.
Second, I suggest you use a finer mesh screen in the bottom of the crucible (cruc), as well as on top of the herb, in the cruc. This not only helps to keep particles from the vapour stream (and the inner core itself), but allows you to invert & tap the unit, to get the cruc out, without the herb spilling out. Of course, the cruc is very hot, at that point, but it cools very quickly.
I rarely use the bags anymore, aside from groups/demos, and much prefer my HA, inverted into my bubbler. This mode is where the HA excels, imo.
Cap I use for bags, and on top of the unit, if I space out my seshes:
http://imageshack.com/a/img196/4309/o9si.jpg
Hope this helps.