Yeah by the looks of it going behind the hairline is the way to go if you can pull it off, which you definitely do!

The difference between injected vs. knots is how the hairs are actually attached to the base. This is what I know about it but I still have a lot of knowledge gaps that hopefully the gurus can help fill in. Basically, injecting the hairs into the base is supposed to create a piece that will look like the hair is growing directly out of the scalp. Some people find them difficult to style because the hairs are more fixed at one angle than when knotted, and the hairs also lie flatter to the scalp, making the hair look flatter. However, the base cannot be too thin because the hair would shed so quickly (injected systems apparently shed quicker and so do not last as long as other skins, and they may not even last as long as lace), so the very thinnest thin skins must be knotted. That said, the problem of knots can be solved with bleached knots. I'm not sure which is more realistic, hair with bleached knots or injected hair. But given your medium density rather than light, maybe this all doesn't matter. Hopefully an expert can chime in here.

An advantage of skin pieces is that attaching is easy. A wide variety of glues should work for long bonds, I would think, such as salon pro 30 day bond. I was planning to go for short-term bonding, using Got2Be glued spiking gel for attachments of a few days. It works really easily with skin pieces for short-term bonding. Hardly any clean-up, washes out with warm water, super quick attaches and detaches. For long-term, over a week or two, clean-up can get a lot messier and take a long time, so detaching before too much time is helpful. But hopefully your dandruff shouldn't be as bothersome now with the piece, since the scalp won't be exfoliating as quickly or as much if you've shaved off a good amount of your own hair and covered the area with glue.