There are 2 modes it operates in - Either you set it to fixed temp, or you have autopilot.  Fixed temp works without any subscription, and you can double or triple tap side of the topper for +1/-1 degree regulation (it will vibrate back so you know what are you setting). Tbh, I am not sure this mode is worth it though, you could just get aliexpress topper that does the cooling for 300 bucks (or 500 for a posh one) or for winter, get a teleshopping electric bed heater for $30.  With autopilot, it's a different story - you set the desired delta ambient, and it will try to keep it as close to set point as possible. If you heat up too much, it will cool more, instead of keeping the same fixed temp of the topper.  It also has a bunch of sensors detecting your breath rate, snoring, hr, hrv and such (different to what i see on my watch, but it is very consistent I must say), and the heating/vibration alarm is really nice as well - it just slowly starts to heat up before your wakeup time, and/or vibrates gently. Way better than getting out of deep topor to the tune of an aggressive alarm. If you sleep good and just want some extra degree of warmth or cool and don't care about all the jazz, there are quite cheap solutions that will do the trick. 

 Sure, this sounds fantastic, especially during the summer.

However, I still disagree with the business decision to charge for the app. The sensors should already be included in the price of the topper, which is a product that the person owns and can’t use to the full extent without the additional subscription. This alone is a deal-breaker for me.