Do have to point out 3 things: $, fill effort, and the hidden work in conversion. $: Are already up to $323 not including shipping (and as the 3 items are coming from different places, will be 3 shipping and handling costs). Lets call it $370-$380 once all the stuff gets to your door. Some places have sold the Discovery package (gun and pump) for less than that (have seen as low as $319) and the P.A. price is within $10 of that.Fill effort: The first time you fill up a 13CI tank, you'll pump your brains out. Normally I never let the HPA tank get under 1000psi, but even so filling from 1000 to 3000psi still takes a lot of pumps (something like 135-165 pump strokes). You get a lot of shots for those pumps. Filling a discovery takes a good number of pumps from empty, but like the HPA bottle, you will usually stop shooting at someplace around 900-1000psi and refill. Filling from 1000 to 2000psi is quite easy with the Discovery, taking from 45-50 pump strokes from a healthy pump.IF you want your pump to have a fighting chance of living a long life, then you need to pump SLOWLY, pump in sets of 50 strokes, then beed off the line, disconnect, and give it a cool down (call it 10min.). Can fill a Discovery in one 5 min. session, no cool-down wait time. To fill a 13ci HPA bottle will take 3 sessions, with two rest periods... call it 30min. the #1 killer of pumps is heat, and heat is generated by pumping without cool down periods. Bleeding the line between pump-sets tends to vent off moisture, and probably contributes to longer gun life as well.So you have to be truthful here... just how patient are you when there are pellets to be shot? A nice long 80-90 shot shooting session on HPA, but a 30min. refill time between sessions? A fast 35-40 shot session with the Discovery, then a 5min. refill for another 35-40 shot session?Hidden work: You're going to have that QB79 at least partly disassembled. They tend to cut up barrel o-rings taking them apart and putting them together. So as long as you have to take it at least partly apart to make the HPA conversion, may as well smooth the edges that cut up your o-rings so the next set will last awhile. Personally, I think if you're going to smooth sharp edges, may as well take the whole thing apart. Either way, remember that dirt/grit/metal shavings are the #1 killer of valves, so make sure it's all as clean as possible.Probably will have that QB apart quite a few times, changing transfer ports, smoothing, setting the spring tension, etc. For some of us, that kind of thing is fun... it just PO's others.Discovery and pump would be band new. If anything turns out to be wrong, can send it back for replacement. Discovery's most talked about fault is the trigger being heavy. Some come out the box with a better trigger than others, and it's possible yours could be fine. IF not, then there are on-line trigger fix tutorials.Basically, think it over.... I like my QB's just fine, but I also like fiddling around with them to get them set up and running right. Like my discovery just fine as well, and it was a lot less work.