I’m about to help two separate friends with rather large wainscoting jobs. It will involve a bunch of sheet goods with a lot of rips per sheet.
I have the tso guide rail connectors and have used them to break down sheet goods before. While the rails are connected it’s really only a couple cuts so I check the alignment with the saw each time and it’s good.

My question is, would you trust the alignment over 1..2...5...25 cuts? Or would you check each time?

A Makita 118” track is something I’ve considered in the past. Since it’s a friends job and we are doing it together, but they want to give me something and buying the track to make the job better would be the perfect contribution, but don’t know how much better it would make the job and the current setup I have is great for what I’ve needed up to this point.

From what I’ve read getting a long straight Makita rail safely delivered is a gamble.

You could reinforce the joint by adding an 18” length of aluminum angle (or even a stick of hardwood) alongside the channel (or on top if not cutting deep), mechanically attached.

I don’t have the TSO connectors yet but I guess it also depends on how roughly you handle the rails. Keep a straight edge nearby and check once in a while and see how long they remain straight.

Im 118" rail showed up with no issues. 

@demographic for one house it is a 100 year old veneered panel we are replacing so those mm might matter, the other is just mdf and I probably could do just fine.

I would probably pick up the guide rail if I bought it, but might take the mechanical attachment advice and see what it does. In the end it’s just a bit more time for a job with a friend and we aren’t in a hurry.