I had a mini oven. Sold it on now as have had kitchen re-fit and now have normal oven. Cannot remember the size of that oven, but I know when I purchased it, and when I a# sold it on I had the full dimensions both inside and out. So, do look for those. Mine was not the most upmarket, I did use my combi microwave a lot, but found it quite useful, particularly for grilling. Not all have a grill function, so if you do want that check that it does. The one I had could just about take in a 12 hole bun tray. Was okay, the temp control was not very accurate, but soon got used to that. Not a fan, which I was used to cooking with, I used to turn round bun trays, etc about half way through.
I think if I was needing something like that now, I would probably prefer to spend the extra and have one of the airfryer ovens.