It is actually better not to have the tongue, as many of these used blocks will not fit back together properly, increasing significantly the waste.
On reclaimed blocks there will be more glue required. The finishing process will start with sanding floors with 24g or 16g abrasives, which means top wearing layer is significantly reduced with first sanding. Gap filling, which will be inevitable, will require double, or tripple the amount that is usually required.
All of the above increases the floor finishing works duration and adds on to the cost.
So, the question will be if the price you are paying for the blocks is good enough to compensate the rest and make it worth?
Sometimes people may consider reclaimed blocks, due to cost (you can find new ones quite cheap), but do not include in their original estimate, the effort and respectively cost of laying and finishing such floor.