is the same (basically) as
NBS is used because it doesn't kill people every time it is transported, plus it's cheaper.
another positive of NBS for radical halogenation is that as the cycle propagates, NBS can sometimes recycle itself, thus only a little catalytic amount is needed.
obviously you'll get many many different results as you're working with radicals from the hv, but you'll get mostly allylic bromination.
i'm pretty sure the high pressure is arbitrary, but it could potentially increase the amount of dibromos you get because of (1/2)mv2
. but that could be looking too much into it.
hv is a sufficient catalyst in an equation. your prof may require you write the solvent but probably not.
markovnikov has nothing to do with this. even if this was X2
you would be dealing with stereochemistry and not regiochemistry. markovnikov only comes into play when your OVERALL reaction shows an H replacing an alkene (note overall because mercuroxidation isn't really markovnikov but overall shows markovnikov characteristics).