The whole stabilize-way was a bit strange for me, I watched some tutorial where I needed to add a Transform and link that to the tracker; somehow, that doesn't feel very "fluent" for me, nor very intuitive.
You see, I often use two trackers - one simply stabilizing, the other one de-stabilizing so it's back to normal again. I can achieve that, but ONLY if I put something in the BG-input on the 2nd tracker (e.g. a back blackground) because the node refuses to work properly w/o the BG input set, but has no option to matchmove the BG directly. Then no options for jitter etc... the tracks itself aren't too bad (much better than AE for sure!), but the node could learn some new things
//edit
And that doesn't even cover the 4-corner-pin. I tried that once, a screen-replacement, and it was... well, weird. I can't even explain it properly from memory, but the filtering and positioning of the points was just strange.
It was from a cellphone, so the display to insert was around 300x500px or so. Fusion however didn't seem to like that input, nor did it like crop-nodes, and it was strangely distorted when applied the tracker. Maybe I have to get a bit more into that, but still it's far from ideal to me