I’ve built spline jigs before. Quick and dirty ones. It was time for me to get a more permanent, better built spline jig. Eagle America came out with the Spline Jig Pro a while back, and when it went on sale, I bought it.
Assembly took about 30 minutes, that included futzing with the camera and fitting the miter bar to my miter slot. The parts are well machined for the most part, with any problems being cosmetic and not impacting the accuracy of the jig.
Eagle America has assembly and usage videos on their site.
Read all the instructions before starting assembly
Don’t fully tighten screws until you’re done with a sub-assembly
Be careful using a screw gun, you’re tightening screws into an insert in MDF
Be careful adjusting the bar to your miter slot – it’s hard to adjust the bar after it’s been installed on the jig
The short screws (there are only two) are used to attach the miter bar to the sled
Well placed holes through the cradle and sled would make miter bar adjustability easier