Dwayne Allen's game log, if you exclude a catch-less Week 2 against the Philadelphia Eagles, is pretty consistent. In his five other games, Allen has recorded either 3 or 4 receptions for between 38 and 64 yards. He also has a touchdown in four of those five.
That average (3.6 receptions, 50.6 yards, and 0.8 touchdowns) is really all you could ask for from a tight end who isn't an obvious every-week starter.
Against the Bengals, though, he's surely start-worthy. The Bengals are one of the worst teams in the league against the tight end and have given up 8.5 receptions, 123.5 yards, and 1.5 touchdowns to the tight end over their past two games against the New England Patriots and the Carolina Panthers.