they have 5 slots just like any other thrall.
kinda useless
Yes, it’s a very interesting feature they decided to implement before having worked on it, because as you said they are useless currently: same number of slots and less HP than other thralls.
would be nice to know if this is going to be fixed by launch
my advice: just assume it won’t…
that way will not be too disappointed if it’s not fixed, and happy if it is.
They will, of course, have more spots as soon as that’s fixed, but for now they’re still not entirely useless–you can wear the backpack yourself (take it off a bearer thrall you own) and get a whopping +5 to your encumbrance stat! That’s as much as an entire set of encumbrance-boosting armor!