The Hilton T5 is an unwalkable 5-10 minute car ride from T5. The HGI is at Heathrow Central and walkable (with train) to T5. You are only there for one night. I have business in the Heathrow area, have stayed in all of the three main HH options, and would not stay in the HGI for a multi night stay. But for one night it is fine, especially should you want to pop into Paddington on the HEX for dinner/drinks.