Pros and cons to them. They do give more counter space. But you need to look at the floor plan they're in. Sometimes you won't be able to access the fridge or pantry with the slide in. Also if you have opposing slides and an island counter with sink then you could have egress problems when both slides are in.
For us out next 5er will have either an island with sink or a rear kitchen. JMO but you can't have too much counter space. We love to cook so counter space is a big requirement. We've had enough of the rear living units with short L shaped counters.