Very happy with my Tacx Flux.

A big part of the question is how important it is for you to have the latest technology. You are comparing a new to market trainer to an old generation of trainer that lots of retailers are trying to get rid of. I think I got 40% off MSRP off a new Flux as Tacx was clearing out inventory ahead of the Flux S and Flux 2 shipments. I haven't seen anything close to that on the kickr core. Basically you are paying more for the kickr core because it is a new product so it demands a premium.

The major downside to the Flux relative to the Flux S/Flux 2 and Core is that it won't support long cage rear derailleurs. Due to the resistance floor of the Flux this is more irritating than it might seem especially for small riders but none of the bikes I use on the trainer have long cage derailleurs anyways. However if I had a gravel or mountain bike with a long cage I would avoid the Flux irrespective of the price difference as it just wouldn't work.