First the cons: as others have noted, it's a bit of a hassle to pick up the keys, and the lock itself is difficult to open. The one bedroom (sliding) door sticks and can only be closed 3/4 of the way. The place is a little old but I found this perfectly comfortable, and a nice break from sterile hotel rooms.
Now for the details!
This is a top-floor loft with two bedrooms on opposite sides of a large common area and kitchen. The building itself is a very old thick-walled brewery, very cool to stay in. The windowsills are a foot deep! The amenities are a bit old and difficult to work - I couldn't figure out how to adjust the heating, so we just opened windows. We stayed in fall, so this worked fine. The bathroom fan is annoyingly loud, but this only runs when the light is no, so it wasn't a problem. The WiFi was acceptable.
We used the washed/dryer, and this worked just fine! For foreign travelers, all the european washer/dryers will lock their door while operating and for a while after heating to let the machine cool down. Either just wait 15 minutes, or if you're in a scramble to get your clothes out, there's an emergency lock release behind a little access door on the bottom right. You can download the manual and figure it out. This is not a comment about this place, just a tip from doing laundry in many european units!
In terms of location, I would say this is good but nothing special. You're not too far from the bottom of the the Royal Road, so you can easily walk up the street to see the heart of Edinburgh. This is uphill all the way since Edinburgh is a hilly place! I would personally rather spend the money to be right inside the old or new city.
all in all, a pleasant stay and good place to work from remotely, and I would really suggest the hosts improve the check-in process and replace the lock and key so it's not so difficult to get in and out!