We bought our first set of TSTs to use on our 24' ViewFinder. We did get dropped signals, but didn't realize then what they meant (that the signal had actually been gone for an hour before we got an alarm.)
Whether or not you'll "need" a repeater/booster depends on lots of things things like how far will your farthest sensor be from your monitor and how much electronics gear (gps, wireless fridge thermometer and the like) you have around.
Interference can come from alot of sources....even those systems that control the traffic lights for emergency vehicles, I was told by a TPMS maker. (Not TST).
Better to have it and use it, even if you don't need it....rather than find out you needed one and didn't have it, IMO.
TireMinder puts a repeater/booster in every set they sell. TST sells them as an add-on. Don't know how much price difference there is.
(For information only. Not an Advert)