Hi C.,
I am not sure how large the arms reach co-sleaper is but here's my input. I have a 15 week old daughter and we started out with her in a Snuggle Nest in between us in the bed but that only lasted until about 8 weeks. We then transitioned her to a cradle next to our bed. I think, or am at least hoping, we will be able to have her in there until she reaches 6 months and has surpassed the 2-4 months critical SIDS period.
That said, when possible I have been putting her down for at least one nap a day in her crib so that she can get used to the room and know that she is safe there. She seems okay with this for now so if possible maybe you can try this approach as another reader suggested. Before I did that though I started taking in there for clothes changes and playtime which I think helped ease the transition so far.
Don't know if that is much help but thought I would let you know that I am in the same boat and also anticipate your other answers. Congrats on in-bed feeding, it is so great and good luck!