I too am struggling with some of the comments on here. Firstly I am unclear why some are suggesting it takes 10 minutes to get from the bus arrival point to the departure gate? Perhaps are people thinking of a non-schengen arrival to a shengen departure? that would be a 5-10 minute walk as the shengen bus gates are around gate 20 which is completely the other end of the terminal. in fact the whole non-schengen area is not massive and you can walk from passport control to any gate within 5 minutes.

the non-schengen bus drop off is on the ground floor around the gate 51a-d area. it's possible the flight would be boarding from one of those bus gates in which case you are there and it will take seconds from entering to being at the gate. the bus gates used in my experience tend to be the new 50a-m ones though so that is up the escalator, about 60m walk, right turn, down the escalator, and then to whicever a-m gate is being used. the OP can download the HEL airport app beforehand to check the gate before reaching the terminal, the buses have free wifi, that walk takes less than 2 minutes. for a b2b there is no security or immigration or bp check on entering the terminal, you just have to walk to the boarding gate.

also as noted if the in bound is delayed the boarding of the outbound will also be similarly delayed. in my experience HEL does not seem to be an airport where they just start boarded with reference to the scheduled departure time regardless and then have you sat in a bus near the aircraft for ages until ready to board.

i have to say i really wouldn't be worried if i booked a b2b at HEL even if it was a bus gate.