I used a similar product in a kitchen for a rental. It fit my budget & timeline, & didn't seem bad for a DIY type floor. I ran screws thru 2 loose floorboards & filled a couple of places where the previous material had chunked out prior to laying the floor. I was concerned about prior issues telegraphing thru. I worked hard to keep the joints tight, but they opened up very slightly over time anyway. No one else seems to have noticed, but that part was annoying.
I would (did) run the material all the way under the appliances. Nothing more frustrating to pull out a range or dishwasher & have it catch & tear a floor that was left short. Plus leaving the old/unfinished floor back there is hard to clean. The added cost is minimal.
If the room isn't square, start & finish with a cut tile, so the taper isn't emphasized by being close to a "grout" line. For example, if the room is 9' 2", start & finish with a 7" tile on both sides of the room instead of a 12" on one side & a 2" on the other. It will look more balanced & the taper will show less.
You can split the difference & snap a chalk line down the center to measure from. That way each side of the room only shows half of the overall taper. Lay some of the tiles without removing the paper from the adhesive strips to get a feel for how they will work if the corners aren't 90 degrees. Sometimes a room will have a side that stands out & shows over the others. If that's the case sometimes it works best to make that side dead straight & let the hidden/broken up sides take up the problems.