Had lunch here with my parents last week; seems pleasant enough, with a good selection of Italian and English meals. Their pizza menu struck me as less inspired than one might find at the best Italian trattorias, but my quatro stagioni was perfectly acceptable. I wouldn't describe it as gourmet Italian cuisine, or the best I've ever had, but it was above average.
The bill for three people came to £48 including main courses, drinks and dessert or coffee, very much in line with comparable Italian restaurants. For myself, I could find better food for the same price, but Allegro was attractive to my parents (my Dad has some dietary restrictions and the availability of plain food is important) and plenty good enough for me. No complaints if someone else is paying, I probably wouldn't take friends here in my own right.
Further to the remarks of other reviewers, we had no problems with rude or unfriendly service on our visit; the service was unremarkable, but adequate to the task at hand. It did not stick out as being unusually good or bad; it is not on the "must do again" list, but nor is it on the "avoid" list. Acceptable if one wants Italian/English cuisine within a stone's throw of Surbiton station, I probably wouldn't travel to dine here.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.