As a firearms instructor I'll say that (obviously) dry firing should be part of everyone's practice routine. But dry firing with an AR can be a challenge. An AR needs to be charged every time you pull the trigger. The Blackbeard system (
Blackbeard: the auto-resetting trigger system for AR-15 - Mantis) allows you to fire away with multiple trigger pulls for an entire training session (actually much longer.) In addition, each trigger pull fires a laser so that you can track your shot or use a shooting practice system like L.A.S.R. (
LASR | Dry Fire Laser Training Systems | Target Practice At Home).
Next Level Training (
Home - Next Level Training) offers their SIRT pistols (trigger re-setting and laser firing pistols) and the STIC accessory which allows you to insert one of the SIRT pistols (currently it has to be a SIRT 110) to mimic the use of an AR. They also sell (or used to sell) the SIRT Bolt, which is their system to convert an actual AR into a laser training platform. The issue with using the SIRT STIC is that it does not replicate YOUR AR. It is basically a generic training platform, though a very serviceable one.
The SIRT Bolt and Blackbeard replace your bolt carrier group and charging handle (and Blackbeard also requires use of their "magazine") in your OWN AR. The difference between the SIRT Bolt and Blackbeard is that the SIRT Bolt requires some fairly complicated (depending on your AR) adjusting to get the trigger to reset reliably with each pull. Blackbeard is drop-in simple. However the SIRT Bolt allows you to practice magazine exchanges, while the Blackbeard system does not (unless you buy multiple magazines, but since they are actually USB chargeable power supplies, they are probably fairly expensive and you probably don't want to be ejecting them onto the ground!)
I've used all three - and like all three. I have used my SIRT STIC extensively (but keep in mind that it does not eject magazines, although you can manually pull them and insert new ones.) All three systems have their pros and cons. The SIRT Bolt and Blackbeard are the most realistic since each let you use your own AR. And each have pros and cons as I've outlined above. It is a matter of personal choice. One thing to consider. The Blackbeard system with a green (brightest) laser is retail $249, the SIRT Bolt with green laser is (was - I cannot find it in stock anywhere) $199. (The SIRT STIC in a bundle with the required SIRT pistol with a green laser is $550 - you can of course, buy the STIC and the pistol separately, or get just the STIC - for $239 - if you already have a SIRT 110 pistol.)
And of course, remember, this dry fire-type training is great for trigger control, sight alignment, rifle manipulation (to various extents as detailed above), etc., but of course there is no recoil to deal with.
As I said, I have all three systems. If I could have only one...boy that's a tough one! (Probably the Blackbeard and the STIC - I know that's two, but unlike Highlander, in this case, there can be two!)
Hope that helps.