I have some MBR partition style flash drives. My pc is in the UEFI mode with USB legacy support enabled.
To use these sticks with this pc not booting off of them such as storage I think I can leave them as MBR but to use them to boot I would have to convert them from MBR to UEFI with the tool which does not damage data during the conversion. They are however empty. Is MBR2GPT the best way or do I need to use third party?
Why bother? When you need them you create them in whatever format you need using Rufus or MCT or DISKPART.
If this is correct, would it do any harm to convert them anyway even if only used for storage in case I want to use them to boot off of? In other words if GPT would they be good for storage and booting?
Again, no point. For data or storage it doesn't matter. If you want to boot from them create them in the format you need.
One of these sticks although MBR was created by Macrium Reflect and does recover images although MBR. Should I leave it as it is to recover images?
Is this a Macrium Rescue flash drive? If it works, leave it alone. Rember, if it ain't broke, don't fix it. 
