There is nothing on the stick that you don’t get with the black box(es)
However in practical terms there are some subtle differences that are worth considering
I use both. Sticks are better for wall mounted TVs that are not near the router, boxes better when near router and if you a a unit to put it on.
The NowTV Voice remote controllers tends to eat through batteries and sometimes losses the wifi connection and you have to re pair them up again together.
One thing i do like with the NowTV & Roku Voice remote is the added bonus of the additional TV standby and TV volume adjust buttons if you can get them to work with your branded television set.
I don't know if you use the live pause up 30 minute feature on the NowTV Black boxes or not, but the full blown Roku Players don't have live pause TV when using the NowTV App.
If this is a biggie for you then the NowTV Stick would be the way to go.
Thanks for @SweetBlitz jogging my mind on another thread about live pause TV.
Also are you a big NowTV Sports pass users, where currently there is no red button Sports bonus streams with the Roku Players, where the NowTV Stick offers Sports Bonus Streams.
Roku would be my choice over the NowTV Stick if it was my money for the little extra outlay.