Playster's Family Plan allows you to stream content on multiple devices at the same time. You can add up to five separate logins to your account with a Family Plan, so that up to five users can enjoy the service at the same time.
If you do not have a Family Plan, you can still connect up to three devices to your account, but you will not be able to stream content concurrently across all three. Instead, you'll be able to switch back and forth between your laptop, tablet and phone without ever losing your place.