EN1

Yes they are worth it as long as you can get in the habit of using it. £500 is a lot though unless it's something special. You can pick up electric ones around £100-£150. I managed to pick up one similar to https://amzn.eu/d/9vay5nR on sale for £70. Integrated sockets aren't worth the extra to me. My preference would be to mount an extension lead underneath to hide them away. You can also get various mounting options for diy like this https://amzn.eu/d/hjQWlwC

I just went through this, but my requirements were strict (needed to be at least 30" in depth). I landed on Flexispot since it fit my criteria and was still affordable. They have a 48"x24" EN1 on Amazon for $109 right now or an EN2 for $159

Flexispot’s fine, but their lower-end models feel flimsy once you raise them all the way up. I had an EN1 and sold it after six months. The frame flexed too much when typing. If you’re spending close to $150, a crank desk or a used Jarvis frame off Facebook Marketplace gives better long-term value.

Do you care about speed, weight capacity, or want a premium top? If not I'd suggest you look at the FLEXISPOT EN1 on Amazon. I had an Uplift, recently got rid of it and switched to Flexispot and for just over $100, it's just as good for my needs. Uplift was faster going up, but you're talking about a few seconds, and it could support more weight, but that would never be an issue, and it's more bulky/heavy. I also have back issues, which is why I got one too. It's not likely to solve your back issues, but it definitely feels better to switch between sitting and standing throughout the day.

I have a Vivo and a Flexispot EN1. Both are solid choices.