I've managed to track down an equivalent product in the US market (foamtapes stock Lamatek products and they don't appear to manufacture an equivalent); Schul Sealtite. There may be others but I've not found them yet.

DL Chemicals Topband & Pressband and ISO-CHEMIE's ISO-BLOCO 600 are products that have English language datasheets if you want more information on what they do.

The crucial differences between these types of products and those offered by foamtapes are:

Pre-compression - Very high compression to ensure that the joint can be fitted during installation without damage and that post-installation, the gap will be effectively filled.

Large range of working thickness - Ensures that the joint can cope with movement in one or both of the surfaces.

25% of the cost of the windows is for the HPE version which is a funky, designed for timber frame product. The narrower versions which don't offer quite the same thermal insulatative properties are much cheaper.

I've seen people using Neoprene gaskets to fulfill some of the joint sealing applications offered by these tapes (Bensonwood use them for sealing their wall units together and to the floor), but I think it's the permeability to water vapour and gap-filling qualities that make them interesting. There are versions that have a working range of 24-42mm (~1" - 1.5"). That's quite a gap to be able to reliably fill!

All in, on paper, I'm very impressed with these tapes. How impressed I am once I come to install our windows remains to be seen! :-)

Edit to reply to Don Wagstaff

In principle I agree, but the reality is that an airtight house will always be easier (read, use less energy) to heat and cool to a given temperature, than a leaky one. Relying on permeability of the walls to provide appropriate air exchange is unlikely to be successful, and using traditional window vents means that window placement becomes critical for air exchange. Managed ventilation (mechanical ventilation or even appropriate use of the stack effect) ensures improved air quality within the house, while minimising heatloss. You can still have a well-sealed house which has breathable (vapor-permeable) walls.