I had some real issues with the correct backspacing on my FS60CB. The Multi-flattener 1.04x requires an additional 31.3mm (I had an old configuration system chart with my telescope so didn’t realise!) the team at FLO told me what I needed, and I finally have the correct back distance and good stars when using with my ZWO 2600. I did have to get an M52-M48mm adapter (OU075) different from the OU002 (this adds 12mm to much) when trying to achieve the correct MTD.
Great experience and super helpful, arrived next day and everyone I spoke to was very helpful. Thanks

This item will be very useful, however I think you should state that when you buy the multi flattener you will also likely need this part too. To make up the correct back focus distance from the camera focal plane.