The last time I saw a quality booster for sale they were $600.00 and made ( I believe) by Haskel?
If you have air but NEED say 4,000+ psi a booster is just about the only way to go.
In the past Altros has made good products, then changed specs over night w/out telling anyone which caused one importer some issues, there response was, .................. .
Buy one and give us all a full review . Lot's of us need more options for air.