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Table of Contents
Magic Lantern's Haunted House of Cards
Incompatible cards
Do not try to use this cards/adapters with ML:
First EyeFi generation
They won't work at all. ML's process of checking for a bootable card is incompatible with EyeFi-firmware (yes, your EyeFi-card has its own firmware). If you want to use first-gen EyeFi with a camera with ML bootflag set: Nope, it wont work at all. You have to uninstall (=remove cam's bootflag) before using such cards.
ML devs aren't able to fix this issue.
All other WiFi cards will work just fine!
SD-to-CF adapters
Frequent issue: Trying to make an SD-card work in a CF-card slot by inserting card into an adapter. Frankly, most adapters are just crap. There are some adapters able to work with ML's method of checking for a bootable card. But most will just get your cam stalled. It is strongly recommended not to use SD-to-CF adapters with Magic Lantern. ML project does not support it and in case of failure you won't get any help.
There is no issue on ML's side using microSD-to-SD adapters.
Micro-SD and ML
Canon Support is adamant about using microSD-cards with adapters for full-size SD-card slot: It is a strict no-go!
For ML it doesn't make a difference: microSD-to-SD adapters do not contain any compontents but contacts and very short wiring. There is no reproduceable performance drop for a fast microSD-card if used with adapters.
Performance will indeed be seen if used with very, very cheaply made adapters where some data lines are simply not connected. I haven't come across such an adapter my whole life. All manufacturers I know ship their microSd-cards with an adapter and those offer a full set of data lines. To be shure do some benchmark runs with/without adapter using a cardreader and your PC. If a data line is missing performance will drop by a huge margin (25 percent and higher).