Hi Adrian,
I've been using it. The Seestar does a horizontal calibration before the first image. It takes between 1 and 2 minutes. Mind you, I also level my tripod and do a compass calibration (where you spin the Seestar around) before each session too. I've actually marked where my tripod legs need to be and set up the same way each time, so the tripod is generally level anyway.
The only time the horizontal calibration seems to have come unstuck is when it was having problems seeing enough stars. It's not a bad idea to do your calibration and autofocus routine on a busy area of sky with some mid brightness stars. It seems to help, especially if you're using filters. Remember that horizontal calibration isn't going to polar align your scope as it's an alt/az setup, but it does help with tracking and finding objects more accurately. I've found that it helps with those pesky trashed shots discarded due to trailing. I get very few of them unless my target starts getting obscured by my neighbour's windbreak trees
