I think with hindsight (and assuming it does what it says on the tin etc), most people would consider that and more, money well spent.
But it's like any 'insurance' isn't it, the 'hope' is that you will never use it and if you do, it comes up to your (realistic / well informed / educated) expectations.
With the likes of Punctureseal (other goops are available etc) I think it's one of those things that everyone should actually test for themselves. You are about to replace your tyres (take it to some private roads ... and assuming you have a good spare ), treat one tyre with the goop then drive it round the block (to ensure it has spread over the inside of the tyre properly). Then set up and drive over the sort of nail or screw you typically find in your tyres then drive it round the block again and see if the object is still there and / or if the tyre has deflated etc. If it all works as expected (and it has for me so far) you can always recover the test goop and put it in another tyre (it's a bit messy but it's not toxic and washes off easily as it's water soluble etc). ;-)
However, if the likes of Continental Tyres supply a tyre pre lined with this sort of solution then I'm guessing there has to be some sort of Commercial support for it (and they are a tyre manufacturer!). ;-)
And that's the big one and where these goops are most likely to do the best job.
Yes, I'm always happier treating a brand new set of tyres for that very reason (VFM etc). ;-)
But like I said, you can transfer the stuff from one tyre to another, should a freshly treated tyre suffer some sidewall damage etc.
I also asked them (on behalf of another mate) if Punctureseal would be 'recommend for runflat tyres and they said a big yes. I've never had or come across run-flats ITRW myself but they explained that should you get a puncture in one, they are really only suitable for getting you to somewhere safe and at a reduced speed. Once you have done that you have to change the (more expensive) tyre and if it was on the front, also change the other front tyre?
So, the theory is that said goop will prevent a (preventable) puncture in the first place and therefore not require the 'run-flat' features.
The other story that I found interesting was they installed Punctureseal in one of those armoured personnel carriers where they can remotely inflate and deflate the tyres, depending on the terrain etc. However, the goop bunged up the pipe work or valves but they said they would keep using it because they found the puncture resistance more use ITRW than the remote pressure system. ;-)
Of course, whilst I'm a happy Punctureseal customer [1], I am not connected with the company and can't offer any guarantees etc. YMMV. ;-)
Cheers, T i m
[1] I first came across the concept with 'Ultraseal' but I think there were issues of both poor copies of the product becoming available and some form of falling out between the original Ultraseal team. The current Punctureseal product is based on the original Ultraseal chemistry but much improved upon (but I may have got any of that wrong).p.s. I have found the main guy (Sam?) at Punctureseal very knowledgeable (and enthusiastic of course ) on his product and very contactable.