I have a Viair portable unit. I'd have to look to see which one I have but I think it is the 440P.
It has been great and will air up my 285s from 18psi to 42psi in about 4 mins per tire. Not stellar fast but fast enough for me.
The only negatives I have are that the included psi gauge is not very accurate when the unit is operating (reads 4-6psi high IIRC) and that the unit gets VERY hot.
I just adjust how high to go (i.e. shoot for like 46psi in the tires to end up at 42psi) when relying on the gauge rather than turning the unit off and on. For the heat, I try to let it cool off before packing it all back up in the bag if possible. If I'm in a hurry I leave it sitting free, away from other items, in the back during the drive home. Sometimes a challenge if you have a bunch of crap in the back.
An important thing to consider is the duty cycle...You don't want the compressor overheating and shutting off 1/2 way through filling up your tires. I bought bigger than needed to avoid that and also so that if others needed to borrow the compressor they could without having to wait for it to cool down.
Jeff Z. (the "not quite as skinny" one)
'97 FZJ80 Antique Sage AE #267, stock
12/74 FJ40, 2F, SM420, 4" Lift, ARBs, 33" MTRs
"...anything else i can do for you guys, how about i wash your car or mow your lawn while you figure out your firewall system? I am now boarderline insane/unibomber." Kipper
"That assumes I'm even capable of pulling and stabbing..." Jacket
"I really like having a detachable unit." Beater