It's a solid 4/5 stars. I stayed for 2 weeks working remotely so I'll give an honest opinion of the pros and cons.
Pros:
-Good location, safe & easy to walk to many places or use public transport.
-Friendly host (I think you are actually dealing with a property manager who is not the owner).
-Well-stocked kitchen.
-Comfortable bed.
-Fast, stable internet / wifi for working.
Cons:
-It can be noisy on weekends as there are bars nearby, and people leave trash on the ground outside so you will be walking through that in the morning.
-Very humid inside (88% relative humidity) like many places in Portugal, and there is no dehumidifier, so you may need to use the air conditioning in the winter to help dry your clothing faster. I think there is some mold growing.
-Manager uses Whats@pp for communication although Airbnb says its app should be used only.
-Doesn't provide some things like hand soap and sponges which I had to buy.
Overall I recommend it for a short stay in Porto.