Thanks @irrlichtproject, I'll order the second one then (is it the v3?). It seems neither block the port (neither user, cassette or joystick port for the first one), because there is a kind of extender. But having a more recent version is better anyway. And I need an external because I have two C64 with different sound chips.

Any reason to get the v4 instead? They are 50% more expensive (but with a nice case), I'd prefer to spare money to order a gotek for my Atari ST.

oh, other thing with the flash/sd carts is to check how much of the disk drive emulation they do. (usually called 1541 emulation after the standard drive)  Some of them only do a kind of 'kernal trap' that won't work with fastloaders.  A lot of music software uses the kernal loader I think, but if you want to run demos/disk games/other things you'd need fast loader support.

the sd2iec is adequate for running sid wizard or music players, but if you need full compatibility i think the 1541 ultimate is the only one that'll do it

For full compatibility, there's also the the Turbo Chameleon 64 and the UK1541, if you can get your hands on one. They're all quite pricey though. Personally, I'm fine with watching demos off a real floppy drive wink

Regarding the sd2iec, external power is overkill imo. You'll only ever need that if you want to do diagnose faulty C64s or do hardware projects (in which case you're probably better off with a 1541UII/UK1541/TC64) or use the thing with a non-Commodore machine (in which case there are probably better options available as well).

I've got my SD2IEC from scitechsuppliesdata (scitechsuppliesltd on ebay), and it's very good, it works like a charm, I can load d64 floppies, but the best is you can have all the data in the sd card (in fat16 format), and load any .prg (like sidwizard) and get the tunes and instruments from the sd card. It's perfect for my use, and the price is fair.