There is a choice of 2 really depends on whether or not you want/need the e-collar.
T20 non e-collar or TT25 for e-collar version. There is no difference in the Tracking part or performance of it, just one has e-collar feature and other not.
I would suggest non e-collar version if you are not sure how to use the e=collar bit as misuse will easily wreck the dog
Garmin are really good at supporting their gear. They did a fixed price replacement on one of my old collars that really was just a pile of bits and 8 years out of warrenty
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