That’s a really good question – both the Mountfield Electress 38 Li and the WORX WG737E are solid cordless mowers, so I can see why you’re torn.

If it were me, I’d lean towards the WORX. The two main reasons are:

PowerShare battery system – WORX has one of the most versatile battery platforms out there. The same batteries can be used across a wide range of their garden and power tools, which gives you a lot more flexibility and long‑term value if you add to your tool collection.
Brushless motor – this makes the mower more efficient, gives you longer run times, and generally improves durability compared to a brushed motor.
In terms of value, the WORX tends to come out ahead once you factor in the battery system and motor technology. It’s a mower that should serve you well now and also tie in nicely with other cordless tools you might want later.

So while the Mountfield is a decent option, my pick would be the WORX WG737E for the wider ecosystem and performance benefits.
Link to my review of this mower below
https://easylawnmowing.co.uk/worx-wg737e-cordless-lawnmower-review/

Hope this helps
Mark