I grew marmande beefsteak tomatoes outside this year - the low temperatures and low light levels made it a very difficult year - I don't think any of my plants yielded more than a dozen decent sized tomatoes, and some yielded half that, so I wouldn't be at all disappointed with your plant if I were you. 
None of my marmandes ripened on the vine - all havng been picked and ripened indoors on windowsills. However, I had some cherry tomato plants in a little plastic growhouse, and lots of them ripened in there - it was noticeably warmer inside than out - I might get another one 