Collet replacement

Hi All,
I need to fit some (expensive) 8mm shank router bits (dumb me bought them and didn't notice they were not 1/4in) into my T-tech TT/R127 (Trend/BnQ hybrid) router. It's a 1/2 inch collet machine. Does anybody think this collet type wouldn't work for this router? You can also buy sleeves which are cheaper, but i will be cutting mortises in Iroko and they come with a warning about using for heavy duty work.

Thoughts - as an alternative, can anyone recommend where i could source spiral-upcut router bits (are these critical for cutting mortises?) for a reasonable price? Also - would it be recommended to drill out the material before cleaning up mortises with the router (would this make the sleeve a viable option as it would have to be doing less work)?

Thanks,

Sean