We have a 10.1+ hand Shetland and just went through this
Okay - DO NOT BUY THE CHEAP HARNESS!!!
We recently got a 10.1+ hand Shetland Pony too. We got the cart and were looking for harnesses.
I bought a cheap one on eBay and returned it the moment we got it.
Then I got another cheap one from the lady we bought the pony cart from. It was brand new and TOTAL CRAP! (ADDED: The second one we got looks EXACTLY like your eBay link…but it had more padding on the saddle. Still no tree though. You’re pony will be miserable in it)
I FINALLY BIT THE BULLET and got the Zilco Shetland Harness. It was the one I always wanted but didn’t want to spend $400!!!
Boy am I glad we got it. The quality and ergonomics/comfort are incomparable. You want a good saddle, breastcollar, breeching and everything adjustable and fitting the right way.
You want pony to be COMFORTABLE. These crappy, cheaply made, thin, narrow things that are closer to $100 are terrible.
Again - I have a pony the same size as yours. I went through 2 crappy cheap harnesses to try to save money. I highly suggest you get the Zilco or Tedex by Zilco “SL” That’s specifically made for Shetlands and THEY FIT PERFECTLY!!!
Our pony is so comfortable in it. And I have so much more peace-of-mind knowing that it’s made to help her pull the cart as effeciently and comfortably as possible.
You wouldn’t believe how ridiculously tiny the cheap harness “saddles” are!?? And the non existant width or padding on important areas (breast, breeching, etc)
Search “Zilco SL” and you’ll find it. Good luck!