Powertank == one more thing to fill. Plus it takes up more space than a compressor.
Speed is not essential in my opinion- well not as essential as space in the SMB or the Jeep. I have run the same Quickair I compressor for years and even a 32" tire take minutes to fill- however it will reset a bead and I've filled many tires from flat to low- just have to sit back and relax.
The only time it's been an issue was after a wheeling trip where some of our group had been ticketed for offroading and I was hiding behind a gas station trying to air up, just waiting for the local PD to roll up and wonder what I'd been doing.
Not that I wouldn't love to fill my tires in seconds, but I'd rather have a fast compressor/tank with an unlimited supply of "free" air, potential breakage notwithstanding.