There are a few potential disadvantages or limitations to using collated framing nails 21 degree:
Requires a pneumatic nail gun
They cannot be manually hammered in like loose nails. A nail gun investment is needed.
Limited angle adjustment
The angle is preset by the gun, so not as adjustable as loose nails if alternative angles are needed.
Potential jamming issues
Collated nails can occasionally jam or misfeed in the gun if not clear of debris.
Length options may be limited
Collated nails often come in standard lengths, vs cutting custom lengths with loose nails.
Waste from cut/broken strips
There is occasional waste if strips are damaged or not fully used.
Strips add bulk
Case volumes are larger than loose nails, so storage space needs consideration.
Material thickness limits
Very thick/hard substrates may exceed capacity of particular nail guns/sizes.
Cost is higher
Upfront costs of guns plus ongoing pricing of collated nails vs loose.
Noise pollution
Nail guns can be noisier to operate than hammers, especially in confined spaces.
So for small jobs, tight spaces, precision needs or limited budgets, traditional loose nails may still be preferable to collated options.