I went down it 18 months ago.
The first section of rocks (only 10m or so) from the visitor centre are un ridable. Then (after the earth path the riders in the photo are on) you have to traverse a rabbit path on the side of a ridge with the bike in your hand and (not enough room to shoulder)it’s a shear drop down to the left (you can see the route going over the top on the photo to where it then drops and hugs the side). After that it goes off to the right on a wide moon scape (the ridge you can see off to the right in the photo) before heading down the remainder. The remainder is made up of former mine workings so there’s a lot of huge boulders that aren’t all ridable hence you’re on off quite a bit (even on the ridable ones I ended up knocking my rear wheel out of it’s QR). The last section to the main road was a bit of a bog then a farm track (nothing special). Having done all that you then have to do the tight & steep switch back climb to get half way back up Maesgwn and then do the bike hike you normally do after the Rangers.
Original question what how does it compare to Rangers, answer = not a patch on it and hardly worth doing (apart from to tick off a list maybe), and don’t even attempt it in high winds (as I did and nearly died).
A better challenge would be to do the double. Llanberis up, Lllanberis down (to the gate), Lllanberis up to the Rangers; Rangers & Maesgwn down. Now that’s worth doing.