This is the better option. I used to have a separate laptop just for one client and it was a pain in the ass. What happens when it gets damaged? They could charge you for the repair. Not worth the hassle of keeping track of it, lugging it around everywhere, keeping it charged & updated. Definitely a pain in the ass. Just do a cloud VM that the client owns with VPN access to the client's network. These are common now with Amazon Workspaces.

Seconded. We use Amazon Workspaces with access to our VPC for an offshore contracting firm we are working with.