USB 3.2 portable SSD on USB 3.1 port

I have a late 2015 iMac (USB3.1, Thunderbolt 2). I want to buy an external portable SSD to boot it from.

This SSD from crucial is optimally USB3.2, Thunderbolt 3 to run at maximum speeds:

However since it is no more expensive than a SATA USB 3.1 is there any reason why I should not buy and use it anyway and be ready for when I do have a more modern machine? Will it give me 3.1 speeds?

Sounds like it should work, as it includes a cable for your situation. Maybe I’m missing your question?

Package Content: Crucial X8 Portable SSD; USB 3.2 Gen2 Type-C to Type-C USB cable (10Gb/s); USB 3.2 Gen1/USB 3.0 Type-C to USB-A adapter (5Gb/s); Quick-Start Guide

Should be clearer, sorry. Will it be as fast used on USB3.1 as an ‘ordinary’ USB3.1 device?