This is a sturdy, excellent quality bed. Unbelievable for the price, a hardwood guest bed that turns into a super king, when using the trundle bed.
I have not put on the supplied castors on trundle bed, so I can fit a larger depth mattress (up to 22cm).

Please note that the castors do not affect the 'erected' height of the lower bed, when its put up the castors are folded away, so attached or not the mattresses will be the same height side by side.