A bicycle is one of the most efficient mean of transport, part of the pleasure we find in pedalling is the (hidden) fact that the bicycle is a multiplier of our efforts, i.e. with the same effort we ride 4 times the distance we would walk.
However, this efficiency comes from design, get the frame wrong and riding the bike will feel like a punishment. This is the difference you feel between riding a BSO (Bicycle Shaped Object) and a properly designed bicycle. Although the BSO is still giving you some 2x/3x advantage over walking, if your body ever rode a proper bicycle, it will feel the difference and it will find riding a BSO an unpleasant thing to do (mostly because of mental expectations).
A dual seat stay tubes system like the one in the picture serves no purpose, a part from making the bike very heavy on the back and therefore giving a cumbersome handling, even to an originally properly designed bicycle.
Since you like the style, you have two options:
- buy a similar bicycle with steel frame and ask a framebuilder to solder the duplicated seat stay tubes: expensive, but you will pay someone real work. I suggest you to go this way if you never rode a proper bicycle, you would not be disappointed;
- have a look for mixte bycicles, they are not exactly the same, but you may get interesting ideas and you may find excellent bicycles (as the Bridgestone Mixte 400 ) or very average bikes as the Schwinn Mirada;