You're staying in a very small student's room in Outer London on a sometimes noisy street. It's about a 15min walk from the nearest tube station, from there it will be about a half an hour trip into the city. You're not going to get clean sheets on the bed or any extras provided (even enough toilet paper) and the shower curtain is something to be feared. You're not going to get much communication or any instructions from the host. Check-in for me was showing up at the house and waiting around for an hour not knowing if I had somewhere to stay until another housemate arrived home and let me in.
All that being said, it's definitely a cheap, authentic London experience. Becoming familiar with the walk back from the station each day and trying the local takeaway shops made me feel like I was actually living in London. You're not going to get a 'hotel' experience but it's a cheap alternative if you're willing to sacrifice a bit of comfort and cleanliness and it definitely beats staying in a hostel.