Snuggle sacks have been brilliant for me as one of my guineas was a jumper and whenever I went to put him back in his cage he would launch out of my hands and I was worried he would hurt himself. For me I wanted to get a balance as I wanted to get my boys used to being handled but not make them uncomfortable or risk injury. I therefore used to pick them up from the cage for lap time but when moving them back to their cage I would put the sack on my lap for them to go in it. When I was moving them from the inside or outdoor run I would put the sack/s in the run and remove the hides so they would run in to the sack. They very quickly learnt that the sack was for moving them and will now just go into them.
So basically, I use them mixed as I wanted to get them used to being handled but balanced this with them being safe and comfortable when being carried around.
As they are now so used to the sacks they can go into them (then within a carrier) when going into boarding, and the sascks stay in their temporary lodgings so they have something familiar with them.