If your worried about restoration costs adding up to more than the car is worth, then using one of these frames starts you off in an even bigger hole than a restoration.
These frame style conversion will require major surgery to the uni-body structure to include removal of all the subframe structure and signficant modification of all the floor panels and rocker areas.
If you looking at a car for resale in the future, these frame conversions also create a limited market as the largest percentage of buyers prefer the stock set up.
It all depends on what you want to do with the car and the budget you have outlined for it. You can make the stock set up perform very well for a few thousand dollars But if you buy a basket case that needs a lot of work, then the formula for completion all changes. I could understand duplicating the factory layout with tubing as it is a lot less expensive than buying restamped original pieces, but these pre-fab frame set ups are pretty spendy right out of the gate.