So the collet adapter arrived today. Fits the Makita really well, as JeffH mentioned I did seat it all the way into the Makita collet. I ran it at speed 3 on the router and I saw no vibration or runout, so from that standpoint it should be fine. I had to raise the Makita up to it’s max height which will likely introduce another problem down the road depending on how often I use it. I would imagine it may be hard on the bearings in the router as the further the distance the greater the force on the bearings due to side loading.
On the plus side this will allow me to use all of the metric bits due to the ER16 collet system. If only someone would machine an ER16 adapter to screw onto the Makita shaft.
Time will be the ultimate judge of this.