I bought a 68ci/4500psi ACI Bulldog as my first post-CO2 tank, and for the first few months I was in love. Having had no previous experience with HPA over my 12 years of on/off paintball playing time, I didn't realize that my new tank shouldn't slowly lose pressure over a few days--until I bought a center flag hyperflow 88ci tank that didn't do that . . . . Then, within two months I had to leave my ACI tank at the proshop for repairs to the regulator . . . .the second time I left it there as a trade in toward another 88ci center flag tank. Upon trading it in, my proshop owner stated that they had been having problems with the 4500 psi ACI Bulldogs, so much so that they no longer were carrying them and were going almost exclusively with the center flag brand for reliability. However, he stated that the 3000psi ACI tanks were not giving customers problems.
Don't buy if there is another option. However, it still is better than CO2