M-Wave Ahead Claw Mounting Tool - Star Fangled Nut

I recommend this product

This tool is pretty faultless and quite frankly a bargain.
My only regret is not buying this years ago as I've done at least 6 star nuts in that time bodging and swearing my way through.
Installation with this took under a minute with little force.

I recommend this product

It is commendable that SJS recommend you buy this rather than a more expensive one.

I have tried making a tool with M6 stainless rod and it bends. It is very difficult to straighten a nut if it doesn't start straight.

With this tool, it is hard to see how it could go wrong. The approx 2" long tube fits snugly over your steerer tube. This is machined so it goes in about 18mm. The rest of the tube is the diameter of the plunger. The business end of the plunger isn't threaded but it is recessed around the pin so that force is applied to the star part of the nut and not the softer threaded part. The tool will set the nut at the correct depth.
The pin isn't replaceable and the tool only works on 1-1/8" steerer tubes, but that's pretty well standard now.