An auto shut off is nothing more than a bit of bent tin and a on-off switch, the only time I've needed to adjust is when the rubber cover wore through and after a move when the arm that works the switch got bent. Many ways to rig up.the downside seems to be that they lack the auto shut off so you can just set it cutting and do something else while it does the work.
Those Rong Fu sound like could be a bargain and if it two for one the parts could be useful.
One thing it's worth mentioning is gearbox oil. Whatever you get check it, change it and run the correct oil. I put in Amsoil synthetic after about 20 hours use because it was all I had in 1986 and it is still going strong.