I bought a NiSi kit. The filter holder is 'native' 82mm and comes with adapter rings 77mm, 72mm and 67mm as standard ... so, in this particular example, it would be compatible with all three lenses straight 'out of the box'.
The "second generation" 'pro' starter kit also comes with a polarising filter, a 10 stop ND, a 6 stop ND, and a soft grad (3 stops) ... together with a few goodies of varying degrees of actual usefulness.
Good things about the NiSi system. The polariser sits rather cunningly within the holder, making the whole thing less unwieldy than most of the competition once a polariser is added (usually as a large diameter filter sitting in front of the rest of the assembly). The filters are glass and should, in principle, be less prone to scratching than resin alternatives. By reputation (not tested by me), the NiSi ND filters add very little colour cast. The market leader (Lee) have a reputation for adding a blue colour cast when used at long exposures. I believe that isn't a major issue to deal with in post-processing and some photographers seem to quite like it. (Anyway, it hasn't stopped Lee from being the market leader.) The NiSi filter holder is a nice piece of engineering, manufactured primarily out of aluminium ... while for some of the competition (Cokin and Lee, for example), the filter holder is made predominantly out of plastic. Once you allow for the cost of buying the polariser, NiSi comes out to be less expensive than the Lee alternative (but it certainly isn't cheap).
Not so good things about the NiSi system. The filters are glass ... one careless or ham-fisted move and that is likely to be about £100 sitting in useless fragments on the ground in front of you. The whole assembly feels a little fiddly. It's fine to assemble or disassemble sitting indoors at a table or, probably, in a warm car. Out in the field with a gale blowing and ice cold hands, I get the distinct impression it could be very hard to manipulate. I don't know if the alternatives would be significantly better in this respect. The 'Wine Country' filter set looks as if it would be a lot less troublesome but you would need to be sure you were going to make a whole lot of use of it to justify its price!
There are various articles out there espousing the virtues of different systems ... and usually rubbishing the alternatives. Unfortunately, a whole lot of this seems to come from photographers who have been sponsored by the brand whose praises they are singing ... with some moving between brands between one year and the next and suddenly becoming fan boys for the same system they were decrying just a few months earlier. It makes it a lot harder to reach a rational decision.
I think the NiSi system is a good one on balance. But I really wouldn't want to make a 'hard sell' for it. You will find proponents of most of the different systems. By and large, the filters themselves are compatible with other systems so your priority should be to get a good reliable holder.
One word of warning ... you may find original "first generation" NiSi kits on offer at very good prices. The first generation holder has a poor reputation ... I can't remember if it's for being too stiff or too loose tbh but, either way, it needed the redesign that it quickly received.
Comment and (constructive) criticism always welcome.