Howdy,
Original machine here vs. the current one, but I would assume this all still applies...
Absolutely make sure to get an edge checker. I do skates for friends, some of which have been sharpened by a Sparx prior to me and its very common to have them have uneven edges. The alignment tool gets to somewhere near, but without an edge checker you can't actually know for sure if your edges are level. So my main tip is to actually check the level after you run a pair of skates and adjust based on what you see. For me, the adjustment will stay true for the same grinding wheel and most others. I've definitely had a wheel where I needed to make 3 to 4 clicks of adjustment when I used it however. I assume the center of that wheel was slightly off the center of the other wheels.
As to the Sparx edge checker vs. others... I have both a cheapo ebay one as well as the Sparx. I would say that both do a reasonable job, but the Sparx one "feels nicer" and is easier to use. The spring loaded clamp is easier than a thumbscrew and the crossbar is a little longer, which highlights height differences slightly better. But it also costs $100 or whatever more than the ebay one so...
I have the cover and like it. Its nothing magical but it fits well and I didn't have to break out the sewing machine. Again, on a budget a pillow case laying on the machine will do the same job, just a little more finicky to put on and won't look as good.
One non-Sparx accessory I really like is the Speed Skate that Wissota sells. https://wissota.com/product/speed-skate/
This helps get a more mirror finish and while I've not scientifically tested, does indeed seem to help glide. You can't do a "finish pass" on a Sparx like a good sharpener can with a manual machine and I feel like this gets you closer to that type of finish.
Mark