I have looked at that Betterly straight line jig and it is just a jig to align rails whilst you tighten them, and at £137 on conbay. Makita do a three meter rail for £200 Makita 194367-7 3-Metre Guide Rail and the only downside is storage and portability, any comments @JobandKnock as you have given great info previously and I know you have one of these. I think it must be easier to have a long straight track rather than trying to join two, just a little out in the middle could be a lot more at the end.