I have an FN TPS, (one of the very best pump shotguns i have had,2nd only to my Ithaca 37 that has been around longer than me)
The factory collasible stock is cheap. But any MilSpec stock body will fit the tube.
And just so you know upfront, The stock tube is solid,
not hollow like an AR 15 stock tube.
The pistol grip is a standard run of the mill A2 AR 15 grip,
You can replace it with any of the better grips made for an AR 15.
The adapter (the chunk of aluminum that bolts to the rear of the receiver, And that the pistol grip and stock attach to)
is high quality.. Right on par with the Messa high tube unit.
The TPS has AR 15 style sights and is already setup to put an optic on the rail.
I changed out the factory stock for an Ace skeleton stock, Swapped the A2 grip for a Ergo Ambi Grip,
Added a side saddle
And the C=More Halo sight. Perfect sight alignment as the iron sights line up perfectly with the red dot,
So the same cheekweld works no matter if using irons or red dot.
The only thing i am waiting for on mine now is the Surefire foward grip/light unit..
And a Magpul winter trigger guard..
ETA. If for some reason you do decide to swap out the factory adaptor,Please let me know as I'll gladly buy it from you.
Almost forgot...The pic...