There are a few negatives to the NFA game...
1. Cost = $200 per item > Not that big of a deal IMO but it does add up the more stamps you get.
2. Wait times > varies greatly depending on a number of variables. Shortest wait I've had was 3 weeks for a mail in form1 about 10 years ago. Longest was over a year for a form3 around the time 41F went into effect. While I will admit, the times suck but I don't worry about this part. I just send in the paperwork and forget about it.
3. Restrictions > NFA items do have some additional restrictions placed on them compared to standard firearms regarding things like interstate travel, other peoples access (no lending it out to someone not on the trust). Once in your possession, you can not just give it or sell it to someone like you can a standard firearm. The whole process has to be repeated to change ownership.
There are some other little things to but probably the biggest being...
4. The principal of it > I find the whole NFA thing arbitrary and unconstitutional. A rifle with a barrel less then 16" (or a shotgun with a barrel less then 18") isn't more deadly or dangerous so why does anybody care? Why are suppressors regulated at all? In this day and age of health concerns about everything, suppressors should be encouraged for everybody to use, definitely not regulated.
That said, as someone who has close to 10 stamps currently (including 2 SBRs), I guess its fair to say the negatives do not outweigh the positives for me.
A lot of it comes down to your own personal situation and needs? The travel restrictions can be a real PITA if you travel out of state often (and to numerous different destinations) with your firearms but if you never leave your state then it really doesn't matter. Suppressors are great, especially for calibers that can be commonly found in subsonic loads like 22lr, 9mm, 45acp, 300blk, etc. but if the only place you have to shoot is a public range where you are going to have to wear earpro anyway then arguably there is little point out side of HD needs?
Because of all that, I do not try to talk anybody into or out of the NFA game. I would just say this... The cost of the tax stamp and the wait times are pretty minor and not a good reason not to do it IMO. Meaning... educate yourself on the whole process and all of the rules and regulations and then figure out your own needs/wants and decide for your self if the hassle is worth it but If at the end of that, the only thing holding you back is cost and/or wait times then I'd say ignore that noise and proceed. The extra time and money is meaningless in the grand scheme of things and will be quickly forgotten.
One last thing, if you are going to go down this path, absolutely get a trust first written specifically for this purpose. Do not file as an individual, or use those "one-shot" trusts. A real trust gives you a lot more flexibility, especially if you have family members that you also want to use or have access to your NFA items or be able to pass these item on to them after your gone.