Steve,
It's Rev. I, not Rev. 1.
The Rev. I TIU is a solid performer. However, I'd argue against it's purchase unless you knew for a fact that the TIU was in perfect operating condition, since it would not have an MTH warranty.
The Rev. L is a much superior product and has improved hardware. It is capable;of providing improved DCS signal strength over that provided by the Rev. I, will support more linear feet of track and has a USB port.
If it were me, I'd pass on any DCS that has an earlier TIU than a Rev. L if it's going to be my main, layout TIU, regardless of price. As a bench TIU, a Rev. I is fine.
In any case, every TIU and DCS Remote is software upgradeable to the latest version of DCS.
This and a whole lot more is all in MTH’s “The DCS O Gauge Companion 2nd Edition", available for purchase as an eBook or a printed book at MTH's web store!