We used one - and Molo still snuggles up with the puppy
(without heat pad or heartbeat now) - its very "well loved" and having resisted for ages, he finally ripped the stuffing out of him last week
We send the puppy with him to kennels when he goes - just like a toddler with its comforter
I don't know if it made any difference to how well Molo settled - he was soooo good, but I'm not sure if that can be attributed to the snuggle-pup or not