ERG mode is completely sub-par, which was enough for me to return this unit after a few weeks of use. I've been on 'smart' trainers for the past 4 years, primarily with the Wahoo Kickr which I love. ERG mode for me is just the smartest way to go for my training which is routinely 4-5x a week in off season and 1-2x per week in summer. The whole point of ERG is that you use an app like Trainer Road, and it does all the resistance changing for you without thinking, without additional shifting. The TACX Flux Smart trainers ERG mode REQUIRES you to also be shifting the gears to get 'close' to the right resistance, and then the trainer will handle the rest. Again - not sure what other people do, but simple training programs like Avalanche Spire go from 140w to 270w (my FTP is 287) jumps for a couple minutes, then back down to 140w. As soon as I hit that first jump, I have to be shifting into the big ring to get the 270w right. Then shifting back down. For other programs that do a very high intensity interval for short duration - say 140w to 400w jump for 20 seconds - forget it. You'll never get the trainer at 400w in time to get anything more than a few seconds in before the interval ends. As a comparison, the Wahoo Kickr does all this flawlessly.
I spoke with TACX customer support - which is another nightmare all by itself. They are in the Netherlands. If you want to work with them over email - which is their preferred method - be prepared for a single question to try and resolve the issue every other day. Meaning - Day 1 - I email them to tell them the issue. Day 2 - they respond and ask me what training app i'm using (that's all they asked). I respond Day 2. Day 3 they respond back saying try the TACX app. I try it on day 3, email them back it did nothing. Day 4 they respond with another question.. You get the picture, takes a week to do something a simple call would get done in a minute. If you want to call them, be prepared for the 12 hour time difference.
Anyway, long story a bit shorter - they confirm that the ERG mode on this trainer requires you to shift gears. It was working as they intended. For $, that's a shock. Save up the extra few hundred and get the Wahoo Kickr to get a trainer that really makes the most out of your precious training time. Or just buy a power meter crank and use a $300 resistance trainer.
Finally - the accuracy. Way off on this thing. I'm using a Quarq PM at the crank. Routinely 8-10% off.. Which isn't cool at 300 watts. TACX conveniently claims that using an external meter interferes with the trainer.. LOL. really? So no way to double check them.. For what its worth, I am now with a TACX Neo, at almost double the price. The ERG works well, the power is accurate (matches my Quarq fairly well), and it's on par with the Kickr in most ways, better in some.
If anyone wants to hear something good about this trainer - its built well, runs smooth. If you didn't care about ERG mode, would likely be a solid choice. Just not sure why anyone who is serious enough to spend $ on a trainer isn't also using ERG mode.
Thank you for your feedback.