The Life Fitness F3 should work. It likely won’t change grade automatically just yet, but it should at least connect.
Please exit Zwift completely then use your official Life Fitness support app to check for updates to your Track Connect console. Once it’s updated, if their app allows you to test your treadmill, try that out. If everything is working, please unpair your F3 from their official app and ensure it isn’t running in the background.
Bluetooth is a bit peculiar in that if an item is already paired in another app, in your operating system’s Bluetooth settings, or on other devices, it won’t pair in Zwift. Please ensure all previous pairings are forgotten.
Afterward, you should be able to open Zwift, switch to the Running section of the Paired Devices screen and your F3 should be pairable. Your surface tablet won’t be able to pair with it over Bluetooth without using Zwift Companion, and there’s a small chance it may not pair with your Android tablet since Zwift is still in Beta.
I did find an article on Life Fitness’ site going over Life Fitness connect and how to pair it in third-party applications like Zwift.
I did a bit of research and while I can find other Zwifters who were able to pair the F3, I’m not finding instructions on how to do it. Keep in mind, there may be a setting in Life Fitnesses’ official support app that allows you to transmit data over Bluetooth that may need to be enabled. If you do have luck connecting, I’d be curious about the cause of the complication. If you’re kind enough to let us know the steps that get your Life Fitness paired properly, we’d be happy to pass along the information to our other Life Fitness members.