When the UPO first came out, many of us considered it to be very accurate except for the Omega emblem. Now, many of us are modding the heck out of the watch - gen dial, gen crystal, gen hands, etc which is costly, but the end results are awesome.
Never got into Tags - thought they were very simple watches. However, seeing this baby, would love to add it to my collection.
Either watch - you can't go wrong. If you're still undecided - get em both