I have the Harbor Freight one and the Tsunami one... both great and I have posted a lot about them in the past.
The Tsunami one (#MV-50) seems to be better made, and is just a bit slower than the Harbor Freight
The Harbor Freight one was bought way back in 2006... and it still works... Used it dozens of times. However, the fuse holder gets really hot and melts the fuse... doesn't blow usually, but I needed to replace the fuse lots of times as it stopped working after it melts the plastic.
The Tsunami I got a year ago, and it doesn't get near as hot in the cable or fuse.
The speed to fill our tires is 6 psi per minute with the Harbor Freight and 5 psi per minute with the Tsunami. A cigarette lighter connected tire air pump
fills at just 2 psi per minute!
So, if you go to 15 psi for sand driving, you take 2.5 minutes with the Harbor Freight to get back to 30 psi... or 3 minutes with the Tsunami... or 7.5 minutes for a cig. lighter pump
(I had a Coleman). When you have 4 tires to fill... speed is nice! I prefer 12 minutes over 30 minutes!!!
The Harbor Freight one was $49 when I bought it, on special in '06... the Tsunami one is closer to $75 I think, but that was last year.