Should I go for the EF EOS R adapter

[mokesl6]

I own a R50 with Kit 18-45 and new Sigma 18-50. I want some lens with longer reach, and targetting RF 100-400mm. But it is out of budget as of now.

EF 70-300 IS is available at 250$ used. Should I buy the adapter at 100$ and get this lens for 350$ total?

Or wait and save up for a new RF100-400?

[jrhoffman75]

It would depend on how long you think it would take to save up and what the lost opportunity cost would be to you.

If this is the Version 1 70-300 it had a defect affecting horizontal and vertical shooting that Canon would correct free of charge. 

EF 70-300mm f/4-5.6 IS USM - Support - Download drivers, software and manuals - Canon UK

If it's not corrected in your lens I don't know if Canon would still do the work.