Have the firestones and they are good, but make sure you get the newest kit, a buddy has the same set up but more miles and his wore through on the bottom. Firestone honoured them and gave warranty but the newer kit has a disc that goes under the bag on the lower spring perch I guess, prevents the bottom of the bag from tearing up. I'm just going to wash mine out regularly at the carwash when I am there to make sure the sand and rocks don't chew it up as bad. No onboard compressor for me, I just use a hand bike pump if I am not around a compressor or gas station. 4 strokes per 1 PSI for my truck, takes less than a minute to go up 15 PSI in each bag. If I'm at home I use the compressor but they will fill very quick if you have the regulator set at 100 PSI+ so be careful. Not a lot of volume in those bags. I have a deck and haul 1 sled plus a ton of gear, fuel and crap under the deck (probably close to 1000 lbs including the deck) and I have never gone over 20 PSI in the bags but they can go up to 35 PSI.
You can "T" the lines or not, up to you, but I like having the flexibility of adjusting each bag separately so mine are plumbed separate. It will make your ride a little rougher but not by much I found, I just air down to 5 psi when not using them and its a little rougher maybe going over bigger dips in the road but not much different just normal driving on flat pavement.
you must have the old ones, my firestones will go up to 90 psi. you must run 5-9 psi in them at all times (empty), if you bottom out with no air in them and bust the mount warranty is void