All I/P trains are new Sm5 trainsets that have some overhead space and also empty floor space for big luggage and bicycles. AC works quite well in those as well. I live along the western part of the route (old M-train) and use them quite often though not daily. With somewhat limited sample size it looks like almost every train going to city center is 1-5 minutes behind the schedule at my home station but they are able to catch up by 1-3 minutes mostly in final stretch between Pasila and central railway station. Little irritating for me, but as long as it does not get worse, not a big deal. I noticed HSL journey planner reserves little more time for transfers involving I/P trains at least for now. Trains can get little crowded in peak hours closer to Helsinki but there should be no problem securing a seat if you board train in the airport or railway station.

Needless to say the direct rail link between my neighbourhood and the airport is great for me. It is hard to say if there is a big enough niche left for the Finnair bus but I guess we'll see.