The polishing kits are fairly labour intensive,and can be messy!
They work quite well on the fine 'swirl' marks that old glass can have,but deeper stuff(ones you can feel with your finger nail) can be a bit trickier.
On really old laminated glass you may also have yellowing and/or de-lamination to contend with.
That cannot be removed.
To get any deeper scratches to a satisfactory level,you can actually end up removing so much glass that you then get distortion/refraction.
The kits work better with laminated glass compared to tempered ,due to the surface hardness.
It all boils down to cost and how much you value your own labour.
They're certainly worth a try.
Personally though,I'd bite the bullet and get new glass where possible.JMO.
