In terms of capability, think of a 7/8 scale 8N. The engine is 24 hp vs the 8N's 27 hp. 1800 lbs vs 2700 (?) for the 8N, plus used 8N's are more likely to come with additional
ballast. Dealers say run a 4 ft rotary mower on a YM240.
In in my experience a 4 ft rotary mower can work it hard in waist-high wet orchard grass if half the mowing is uphill as in my case. But I think putting an 8N's 5 ft mower on the 240 will get more acreage done per day than a 4 ft and won't strain it if you take a partial cut in the heaviest material. YM240's compound low gears are a definite advantage over 8N especially for a rototiller, or for creeping up to a pallet using front forks etc. And it can maneuver better in tight spaces. They are narrow, I added a ROPS and water in the tires before I felt safe on side slopes.
I think the only point where an 8N is clearly better is discing - its added weight for traction and its 3-point lift capacity are greater.
The advantage of a YM240 is that its bulletproof. No tuneup, nothing to tinker with or maintain, and it will run like new for years. There's nothing breakable; I made every sort of idiot-new-owner mistake and never broke or wore out anything in ten years. You seldom see posts here about repairs beyond keeping the cooling system maintained etc.
Don't know if you are aware - Yanmar entered the US market in the 1970's parallel to Kubota and YM240 was a model they sold here for several years through authorized dealers. Then later Yanmar contracted to build Deere's compacts and ended US sales until their recent re-entry. Yanmar-USA still supports this model with legitimate factory parts. I like to think this specific Yanmar was what spooked Deere into contracting Yanmar to build for them, instead of designing their own compacts in-house, they recognized they couldn't exceed its quality.
Now today a huge number of YM2000, the Japan-market version, have been brought over and a healthy replica parts market exists here selling NAPA quality replacements. So YM240 has both factory and 3rd-party support.
I see a MF265 in your profile. Think of this as a smaller sized version of it. I'm certain you will love the YM240 as soon as you get the prior owner's confusion sorted out.