When you say “constant”, I hear known lower and upper bound which are the same number. If that’s correct, I would use an array personally, there seems to be no downside.
BoundedArray is more for a known upper bound, but where the actual number of elements is runtime-determined. I’ve never had occasion to use one actually, it seems like the idea is that it can use the familiar ArrayList methods but with a stack allocation of constant size?
I’m sure that can be useful, but if I need to store exactly sixteen of something I use a plain-old-array and a separate index. Might be force of habit from other languages but it works.