Reciprocating Compressor

It isn't feasible to go from ambient to 150 bar in a single stage. For one thing the mechanical design for such a large single stage compression ratio would be problematic; one has to allow some excess volume to accommodate valves. More fundamentally, the temperature of the air at the top of the piston stroke would be extremely elevated. I'd have to dig to recall the formula and do the calculation, but I think the adiabatic temperature for compression to 150 bar would be upwards of 1000 C. So the air has to be cooled as it's compressed.

The usual arrangement for this sort of compression is multiple stages, with intercooling between the stages. If you're looking for something small and cheap to fill paintball cartridges, just go with the Shoebox compressor and a small shop compressor.

If you're wanting to fill scuba tanks, that's a different story. The Shoebox web site mentions filling scuba tanks, and perhaps their compressor really is safe to use for that. But I'd be very cautious. A scuba tank compressor is a very specialized piece of equipment. Vapors from oil-lubricated seals in a compressor not designed for scuba can kill a diver. Not to mention the fact that bypassing the safety protocols followed at reputable dive shops can get you killed in a tank explosion.