If you have to do lots, then it's a great help.
If you only need to do one connector, then the setup time means it's probably quicker to do things manually, especially if you can just use Z-tape to attach the new FFC.
The results from the machine, though - they're perfect once it's set up right (and bear in mind, you may need to buy suitable thermodes for every job, so there's a lead time. It depens how much space there is around your connector as to whether you can use a too-big thermode).
I got mine from a company that had been using it to rework failing LCD monitors. They were very pleased with it, but the contract had come to an end.
Are you sure your replacement FFC wants to be soldered? Not all of them have suitable materials, and can just melt...
At the moment, I'm using FFCs with stripped back plastic, so the only thing for the final 5mm are the conductors, but I have also soldered more normal cables. You do need to avoid stiffeners, though!
If you can put up a photo of your job, I'll have a look...