Booster Pump

Nothing to do with dangerous or expensive. There's a lot of compressor that will fill 5-8 times faster than a booster. No one wants to wait 10 hours to fill their tanks and 1-2 hours for top off. There are affordable compressor that will fill a tank in about an hour and top off in 15 mins or less. So why go booster. But that's just me. I can't wait over an house for a top off. And half a day for a fill. 
 
You asked why they can't keep booster on sale. I'm giving you some answers. There's probably other answers why they aren't popular. One, they are slow. And two they need an oil-less shop compressor to feed it. With so many affordable compressor right now being made that doesn't need a shop compressor to fill to 4500 and can fill 5-8 times faster. That's main reason I believe no one is interested in these booster. If you want a booster that doesn't use electricity. Check out the air venturi booster. Pyramid air used to sell it but it didn't sell well and they stop selling it. Or I can't find it on their site anymore. Also the shoebox f10 is also a booster. It needs a shop compressor to boost the 100 Psi to 4500. 
 
...the air venturi booster. Pyramid air used to sell it but it didn't sell well and they stop selling it.

The price of the AV booster was $600 after discount. It's official value proposition is "... With it's light weight, compact size, the Power Booster is far less expensive than a more conventional, stand-alone high pressure compressor...." 

I think this does not stand anymore when you can buy a standalone 4500 psi compressor today at less than half of the price ? 
 
You can get one from Altaros is less than a week. Flawless QC. Maybe try typing them in the search bar on this forum.

Doesn't seem like shoebox is selling these days? Personally greatly prefer the altaros design anyway.

John

Mine took seven weeks to arrive. Czech postal service, not Altaros's fault. After approximately 50 hours of use, about 2 full fills and half a dozen top offs of my 6.8 CF bottle, It needed new seals on the high-pressure piston because it wasn't lubricated properly when it was assembled. It is painfully slow and it needs DC power to switch the valves. It also uses a lot of air and I burnt out my 40 litre home compressor, keeping it supplied. It can be used to cascade from a half-full bottle but it will still require a power supply and an input compressor to drive the pistons. Other than that, I'm happy with mine and the company support is excellent apart from the language barrier. These days I only keep it as a backup. I don't think that this is what the opp has in mind for his requirements.
 
Yep I saw the Altaros but needing power is what turned me off. If any one is not familiar look at Bob Vogul Mr.Hollowpoint YouTube pcp booster pump. you cascade from one bottle to another no elect required. I have a chinese compressor but 2 45 min tanks don't keep up with the big bores without having to stay plugged in and constantly topping off my bottles. The pump appears to be a Haskell type air amplifier. People that have these are bringing one bottle all the way down to 1300 and can boost to 4500 with a 150 psi driving the pump. This is very practical to me with my guns requiring 3800 to 4500 2 or 3 fills and i'm done without busting out water and pump.