From reading articles (Joe Friel and Hunter Allen) my understanding is that fluid trainers don’t have a lot of “momentum” and therefore don’t feel very “road-like” unless you spend a lot of time climbing at slow speeds (like on a MTB trail). Smart trainers like the Kickr come with a big flywheel to offer more road-like feel - more momentum so pedaling feels natural.
If you ride outside, then the Kickr feels pretty natural. If all your riding is on a fluid trainer, it will likely feel different.
That said, my Kickr supports Erg, Resistance, and Standard modes. Wahoo’s Standard mode is “Just like riding on a fluid or wind trainer, the faster you go, the harder it gets.” I’ve used standard mode recently and actually prefer it to Erg, especially for zone 2 rides where I include a handful of 5-sec sprints. Erg is nice if you want to mentally zone out, and just turn the pedals without a lot of active mental engagement. Erg is also nice on vo2 intervals as you can’t give up, because if you start to crack then it is possible to fall into cadence downward spiral and grind to a halt.
Regarding road-like feel… I find Erg at sweet spot and threshold to be somewhat comparable to riding outside. Last night I did a well paced 50 minute threshold session outside, on flat course and into a headwind with something like 50x17 or 50x15 gearing. Power variance looked like this:
Average power ~245W and standard deviation of 25W (according to WKO5). Standard deviation is a measure of power fluctuation around the average power.
Haven’t done much inside training lately, so I pulled this up from last year and again it was in a similar gear:
Average power ~225W and standard deviation of 12W (WKO5). That is pretty much the same as a recent Truuli opener done at higher average power but same standard deviation.
Power fluctuates less on the trainer, when using the big chainring. However it feels similar enough and no real difference from an adaptation point-of-view. When I switch to little chainring the power is so smooth it feels unnatural.