You
are going NFA, right? With something that nice, it's the only way to fly.
Worth depends on how nice the price is, but if you've always wanted a Swiss model, you won't regret it.
Between a 553 and 551, I chose the 551, but only due to barrel length and ballistics. If you're not likely to use it as a weapon I'd definitely go for the 553. It'll be more fun. Lighter, handier, louder. The 553 is great for the CQB role, of course, and reaches farther than a SMG/PCC.
If you later decide you want a longer barrel (you won't) lol, you could swap a 553 LB (Long Barrel, 13.7") onto it, assuming you can source one. Those look goofy to me though. The 2 benefits of the 553 LB compared to the 551 are lighter weight (although you don't get the longer sight radius or rail length) and the ability to launch rifle grenades.
Their diopter sights are among the world's finest, if you enjoy irons.