Great info from 42x16. I don't have any experience riding a smart trainer (literally none, not even tried one in a shop) but there's a couple of thing you might find useful I can say.
The Tacx Neo has a strange issue. There is a bearing in the flywheel that requires a 24 spline ring nut tool to access. These tools are pretty hard to get hold of and they're expensive. I know of a couple of people who have had this bearing fail. I think Tacx sent both of them a new flywheel, so they will sort it, but it's a bit of a pain. This may also be the case with other direct drive turbos, I have no idea. Both of the one I know of failed within, I think, 10-12 months of heavy use. The load on these bearings is going to be high, so it's not hugely surprising they need replacing. Something to think about when deciding what to go with. People I know seem to either have Tacx or Wahoo smart trainers. That's possibly because those are ones stocked around us. I have Elite indoor training gear and it's been fantastic.
as 42x16 says, it depends on what you want to do. I've found speed/cadence sensors and a dumb turbo with Sufferfest are more than enough for training. Watts may not be accurate but they are reproducible which is all you really need for training. I also use rollers which have a measured power curve so speed/cadence works for that. This won't give you the full benefit of erg-mode but you can still do proper workouts just by shifting gears. Your ability to control your cadence is a bit limited doing things this way, that's probably my main complaint other than it feels a bit weird riding at 70rpm in 50-14 when there's a climb in the video!
If you want to use Zwift them I think you do need a turbo that measures power to get the best out of it, but you can still ride it with a dumb turbo. I did it during my trial. I wasn't a fan of the computer game style of Zwift so stuck with Sufferfest, but it worked.
I have an Elite Volare Mag turbo and the Elite Quick-Motion rollers. The turbo works perfectly for what I want. I know which level of resistance I need to set for the different Sufferfest videos I ride and the power numbers are reproducible enough (as long as tyre pressure is the same) for me to use it effectively. The rollers are absolutely brilliant. I've used 4-5 different types of rollers from Elite and other brands. These particular rollers absorb movement of the bike and it makes them extremely stable. This means I can do out of the saddle riding very easily, sprints feel a lot safer and so on. Highly recommended if you go that route and they do make a smart version that works in erg mode, although the heat generated can effect power readings according to reviews on YouTube.