Haven't been on it, but I imagine if you plan to check your bag, you'll have to go to ABE, as there wouldn't be a way to get it in EWR. Also (I'm guessing) if you bought a round trip ticket and don't show for the bus, your return trip may be canceled. The bus leaves from Gate C71, same place as the bus to Terminal A.

Weird thing about this "flight" is that if you look up flight status and put in EWR-ABE, it gives you the three options, indicating that they're bus service. But if you click on Seat Map, you get a picture of a six row Embraer RJ145! Also, the OP mileage is shown as 67 miles!! Is that the shortest segment in the CO schedule?