We had a great stay ar Helder's apartment. It's very central, perfect to walk around, and close to restaurants, public transport and a small grocery shop. Helder left us some goodies for our arrival, which was very kind.
The apartment is spotless and had all kitchen utensils we needed to prepare breakfast. The sofa-bed was comfortable enough to sleep for 4 nights. The apartment might be a bit too tight for 4 people, although for 3 of us it was big enough.
Helder has offered us a private shuttle from the airport and I can't recommend it better. Pedro picked us up, gave us some good tips about the city and most importantly helped us to bring the luggage up to the 4th floor. You can't drive on the apartment street so be aware you'll have to carry your luggage at least half a block + 4 levels up. I recommend the private shuttle.
The only downside of our stay was the noise coming from the street and from the unit below. The restaurants shut at around midnight so the street noise doesn't last for longer than that, but it's impossible to not wake up at 3am with the garbage truck at our door. We also weren't lucky with the guests downstairs being very loud during the night. The insulation between apartments isn't great, so I recommend brining an earplug - it worked fine for me.
Overall I recommend staying Helder's place and I would likely stay there again on my next trip to Lisbon.