The prewarming of the intake air is not a factor for a typical gas burner assuming the air/fuel mixture is properly setup.
MOst of the concentric units blow the exhaust out towards a different direction versus where it pulls in combustion air. If it is oriented properly, it shouldn't have any effect on the efficiency or operation of the unit.
The exhaust I have is sort of a hybrid. It's one piece on the exterior, but uses two separate pipes through the wall. When the contractor installed it originally, they did not follow the instructions and the exhaust's moisture on a super cold day condensed, dripped down, and froze over the inlet, shutting the unit down. I verified with the manufacturer that they installed it wrong, they swapped the inlet/outlet, and it's worked fine for years since.
In our condo complex, many of the units use a Trane condensing furnace. THey use a similar device - two pipes through the wall into a single device. Those blow the exhaust out straight, and suck combustion air in around the base so there's minimal cross-contamination of the combustion air.
Using a snorkel may be slightly less money. I see no reason to go that way unless you really want to. This all assumes that the device's instructions allow the concentric system (all that I've seen, do).
