My tuppence worth - of the guns mentioned I own -
P15 .22 - very light, short, short length of pull, big shot count, accurate and damn near silent with a carbon shroud. Lane and Huma both do regs for them - cocking lever in a bad place unless modified
NP-02 .177 and .25 - short as the P15 until you put the very necessary moderator with a long length of pull, accurate, decent shot count, heavier than it looks
Empire XS .22 - very short, heavy but the weight is it at the back, about 120 shots, the moderator (it's not a shroud) may need aligning correctly if using a secondary moderator as they can suffer from clipping (not on the supplied one but one fitted to the end of it), accurate - can be regged if required - set up properly this should double the shot count
All four of mine are capable of repeatedly smacking golf balls at 60yds + (.25 takes a little while to get there mind

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Size comparison (top one is a Kral Knight semi-bullpup)
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and the XS against the P15
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