Hi, for 0.7 acres of rough ex-farmland with weeds and thistles, here are my thoughts:

EGO mowers are very good - excellent build quality and powerful battery systems that can handle tougher conditions.

However, for your terrain and size:

- Robot mowers wouldn't cope well with the rough ground and weeds, though some models coming out next year will handle rougher terrain better - still early days though
- Ride-on mower would probably be your best option for 0.7 acres with challenging terrain like yours
- I just completed a review of the WORX cordless mower but it's designed for lawns up to 1,200 square metres (0.3 acres), so too small for your needs, link here
https://easylawnmowing.co.uk/worx-nitro-wg761e-80v-cordless-lawnmower-review/

Given your mix of weeds, thistles, and wild grass on ex-farmland, a ride-on would give you the power and efficiency you need for that size area.

Best regards
Mark