There's a fellow at our club who effectively makes his own, only with birdshot, by pulling the shot and power piston, adjusting the powder load (down slightly), cutting the power piston down to just the cup, then re-inserting the cup and shot, cutting off the excess plastic from the shell, and using a card to cap it all.
Bit of a finicky process, but he's got it down to a science and they'll cycle reliably out of his Benelli M4 3.5" super magnum. He has the mag tube blocked for 5.9 x 3.5" shells, and with his custom loads, he can cram 11 in the tube, one in the pipe, and a normal length shell ghost loaded on the lifter. Heluva an advantage in 3-gun matches.
If you have a specific gun you're thinking of using these in, I would almost recommend going with the hand-load route. You can fine tune the load and length to exactly the point it runs reliably in your gun, rather than buying the Aguilas and hoping for the best.