I like the Bauer brand because their parts are durable and readily available, and they have service techs all over the world to support them in addition to the factory staff. I have seen Bauer models that last 30-50 years with proper maintenance, which reduces their cost overall. I agree with Rjack321 that a Mariner/JrII would not fill be sufficient 40 tanks a day. Here's how to do the math to figure out your minimum compressor size: Multiply # of tanks/day (40) times the tank size (80cf) = 3200. Divide 3200 by the charging rate, and then divide that by 60 (minutes per hour) and you will find how long it will take to fill your tanks daily. So for example, the Bauer Divemate with a charging rate of 8.4 would fill 40 tanks in 6 hours and 20 minutes. The DiveMate E3 (Three phase electric) is just under $9000, and the Gas model is about the same. If you wanted to go beefier, I would look at the Bauer K150II block, such as the Vertecon VTC 20-E3 with a 21 charging rate at $22,000 which shortens your fill time to about 2 and 1/2 hours. Think about the cost of your staff when you calculate your fill times- if you go with the manual drain, you will have to have staff to do it, whereas with the ACDrain, you won't have to babysit the compressor.