At £20 a night, for two, being right in the centre of the old town, you cannot complain. The beds are lumpy, the apartment is a bit grotty, but it's OK for say, 10 days. The staff are nice, but oddly, hardly ever there, even in the posted time periods they are supposed to attend. It may be worse in the winter season, but a lot of people simply cannot get in to check in, even if they arrive in the 'staffed' periods of 12noon to 8pm. If you miss the opening times, or if the staff have gone away (normal) you will not get in, booking or not. The staff are however friendly but mostly unable to deal with problems - like missing kit in the rooms, broken showers, broken room entry doors, broken showers etc. We hit lucky compared with 2-3 people who also stayed but had many issues.
As for the €100 breakage deposit, as far as I can tell, this seems to be a "holding payment" that expires on its own, so there is no "return of deposit". In any case you'd be insane to not use a credit card (which gives a lot of protection).
The building is obviously being "camped in" by the owners, hoping to make a capital return on a future sale, or maybe looking to get a deal to sell - this may be why the apartments are so obviously under-invested and run on a show-string.
On the other hand, we were OK for only €20 per night, as we were there partly for appointments, and it was only partly a holiday.