I used inspectrum mainly with raw IQ-files from gqrx, so the c16 format is indeed correct.

For me, the great thing about the tool is that it is very visual. (*)

It allows you to get an idea what kind of signal you are looking at (on-off, FSK, PSK, …) and get a rought idea about timing. That then gives you information to better apply the proper filtering in urh and work from there on. It also allows you to see any “abnormallities” … e.g. I once came across a signal that sounded to be two-tone FSK, but after closer investigation, you could see that the two tones overlapped (in the time domain).

Concerning the bitstream you demodulated, I am not at all an expert in SIGINT, but I guess we can do some basic research like repeating pattern (that could indicated a start of frame), maximum number of consecutice all-0 or all-1 (that can indicate bit-stuffing) etc. The problem with unknown digital is that the number of variations of different processing-techniques is almost infinite: scrambling (not encryption, but scrambling) , FEC, …

(*) The visual element of inspectrum is the reason why I use it in a workshop I give. The workshop I do is similar to the one done by Mike Walters that is on youtube: www.youtube.com/watch?v=tGff31uGXQU