This is overall a very good deal you are getting for the price. Try to find any central location like that in Istanbul for that price and most likely you won't get any. So, the price is well worth it. While the facilities are quite old - they are done in a stylish style and this is what I loved about it.
Now, the few things you need to be aware about... The neighborhood. The streets that are right around the house are not the prettiest and probably not the safest, I was harassed by some guy while walking at night (I wasn't hurt, but didn't felt comfortable). If you are streets smart - it's just 1 sketchy block.. And then there are many hotels around with a similar situation. It's Taksim, so...
Wi-Fi. It was not a good connection, quite slow. I didn't texted the host since it was manageable for me, but for any serious work it's too slow and unreliable. Needs to be improved.
But again - for that price you are getting a great accommodation and the host is super fast to respond!