One EGT is better than none!
The problem of course is that you don't know if one (or more) cylinder(s) is (are) running hot and if you are using the EGT to operate at LOP then that substantially increases the danger of causing severe damage.
With a single EGT I think you are better off using the mixture control but back it up by a reasonable degree so the engine is running a little more rich, and by all means monitoring the EGT to establish whether it trends as you would expect.