I am a solo female traveller and have been in the UK for two months, so this is a review from that perspective for a long term stay (a little over two weeks).
First off, I cannot say enough good things about the location of this place. WOW. The Clerkenwell/Holborn/Islington area is just amazing--bustling yet quieter than central, easy access to literally everything, great transit connections, you name it, it's there. Lots of good grocery stores and restaurants and coffee around, and easy to walk to various libraries, museums, and Euston and Farringdon stations all in between 10-30 minutes. As others have said, it is pretty noisy at night--lots of sirens--but I got around this with earplugs and a white noise machine (and keeping the windows closed). And as a solo woman, I never once felt unsafe in the area, even walking alone at night. It's well lit, there are people around, and I felt confident that if I had any sort of emergency Ali would respond quickly. The views are really lovely, too, and the kitchen is relatively well stocked--I had everything I needed to make my own meals, store leftovers, wash my clothes, etc.
Second, Ali is a great communicator on the whole and went above and beyond for me at check-in especially. As someone staying in the UK long term I had a lot of luggage and food I was moving from my previous flat, and was afraid of carrying all of it around London for 6 hours between accommodations. Ali went way out of his way to get me into the flat REALLY early--that is, at like 9 am, before he had to go to work. I'm grateful he was able to arrange it, because it made things so much more comfortable for me and I didn't have to spend a whole day lugging around my entire life. He was also really easy to get ahold of via WhatsApp and responded very quickly when we needed to make various arrangements. And generally, there was none of the extra rules (like "change the sheets" " wash the entire flat" "sweep the floors" garbage) that so many airbnbs usually do, so I really appreciated that I didn't need to pre-clean the flat before I left.
The only things that were slightly off--but again, nothing worth docking major stars for--1) The floor kind of tilts inward which is not really a problem, except it makes the bed kind of uncomfortable since you're sleeping tilted (a problem for my back, as a stomach sleeper). The bed itself is great. It's just the floor. lol 2) A few days after check in they had a showing for the flat to a long term renter. I was told I could stay, but I felt awkward about it and decided to leave the flat instead. Just weird to feel kicked out of a place I'm paying to rent, especially during two pandemics. I understand the situation (the prospectives were only in town for a few days), but it was still a weird experience. 3) I checked several weeks in advance to see if I could check out a couple of hours later than 9 am because of my luggage/next accommodation's awkward timing, and they said no problem. But then two days before I was meant to leave it was suddenly a no-go because another guest booked the flat and they needed to clean it--never mind my previous arrangements and the fact that I made travel plans around a late check-out. They pushed the cleaner back to 9:30, but then the cleaner showed up at 9:20 anyway, so I ended up rushing out and sitting at a train station for an hour and a half with all of my luggage when we had agreed weeks in advance that I wouldn't need to do that. So while I appreciated the attempt to push things back, it was still frustrating.
The only other thing I think is worth emphasizing is the fact that it IS a penthouse--it's up a LOT of flights of stairs and there is no elevator, and it gets hot with the windows closed in the summer. It was ROUGH getting all my luggage up by myself. But once it was up there it was totally fine! And leaving the windows open while you're in the flat cools it down quickly since it's so high and there's a cross-breeze. I have no real complaints about either of these things, especially because the lack of aircon is standard in London, but you should be aware of this if you have access needs.
All in all, I would say I had a good experience at Naseem and Ali's place. The location overrules everything, so if you're looking for a well stocked place with a communicative host that's central, this is a good spot.