I don't own Mrodair, but I see on their website that their stuff takes 2,900 - 3,300 psi fills. The 3,500 psi SCUBA tank is not going to fill your gun many times at all. You really need a 4,500 psi fill tank to be satisfied.
http://calc.sikes.us/2/index.phpPer Lloyds fill calculator - an 80 cu ft 3442 psi tank would fill a 100cc reservoir from 1250 to 3000 psi approx 24 times. Your actual fill count will vary depending on your ideal fill pressures and actual supply tank pressure.
First off, if they are aluminum tanks, they are 3000psi max. Steel tanks go to 3400psi.Scuba tanks are all I use and they work terrific. See guns in my sig. I own one steel 80cuft and rent 120s when I go down shooting in Cross, SC. I won't take a 120 down below 3kpsi in a day of play.Downside is I don't think they will fill them for you w/o a Scuba certification. Check with them, but I think it's required.
Not sure what the size of a Varmint's air cylinder is but:An 80cuft tank with 3440psi, will fill a 185cc airgun cylinder from 2200 up to 3000psi= 28 fills
Downside is I don't think they will fill them for you w/o a Scuba certification. Check with them, but I think it's required.
If they have a current hydro and if your scuba shop will fill them, go for it. You'll still be able to fill the gun quite a few times. IMHO, save your money.You should note that they have to make changes to their compressor to fill to 4500 psi. My scuba shop complains, you have to leave it and it costs triple what a 3400psi fill does.