I find it interesting to see that others have suffered with problems associated with expansion/contraction using recycled plastic on their lines, I thought it was perhaps only me. However after first coming across this problem a couple of years ago I have found a way around it.
The first part of my plastic supported track was laid using 3 metre lengths of plastic plank, where the expansion / contraction issue was really quite severe but this was solved by simply leaving much larger expansion gaps in the track (approximately 4mm). The next part of my line was constructed by cutting the top board into slices purely to allow the curves to be generated, but this had the effect of considerably reducing the expansion / contraction problem with the added bonus of allowing rainwater to run off more easily.

As time and enthusiasm permits I will do the same with the 3 metre lengths of boarding to make it look the same and prevent the pooling of rainwater which eventually allows verdigris to form and look unsightly.
Whilst I have to agree that Filcris is not the cheapest way of constucting a raised track, if properly arranged it does mean that there is zero maintenance and as I get older is something that I really value. Also as the garden grows around it, I think it blends in quite well.