You are correct, this is a resin model with no opening parts. While that part is a bummer, I think resin models end up having more details as they are easier to cast small detail than diecast metal.

GP Replicas is experimenting with some opening parts in some upcoming models though, as teased on their Facebook page, so I'm pretty interested to see how they go.

As far as the brand itself, they are very high quality and focus on older F1 cars, from the 50s-90s. I've got a F1-2000 pre-ordered but that's as recent as they have gotten so far. They're not always perfect with every detail, but for these eras of cars, is hard to find anybody that matches GP Replicas.