IMO, right now things are on the cusp of another full-blown black rifle panic like we saw late 2008-mid 2009.
What happened was that just about all AR parts were in high demand and the parts that require great care (barrel, bolts) were well-night unobtainable. So if you see what you like in stock now, just get it now. Most companies stepped up their production a bit since then, so stuff comes back in stock more often, but it still sells out.
I'd find the stuff you actually want, if it's in stock then order it, but if it isn't, then use the "email when back in stock" feature (if they have one). When you get the email, jump on it.
I remember BCM uppers and BCGs selling out in less than an hour. You had to move FAST when you got the email.