I'm new to the sky3ds card myself - ordered it last weekend from 3dscarduk.com and it arrived 3 or 4 days later.
I'd recently upgraded from my original, launch day, o3ds to a n3dsxl, and had waited until that arrived to see what fw it had on it before choosing either gw or sky (fw was 9.4
)... system transferred old 3ds to new 3ds (which required fw update) - also treated the new 3ds to a 32gb micro sd, which meant that I'd got a spare 4gb (Toshiba) sd card that had come installed in the new 3ds.
I spent the few days between ordering the sky3ds and it arriving preparing by reading up on it's operation, downloading roms (which was easy - I got probably every game I'm even vaguely interested in playing over the course of a couple of evenings - over 50 roms, predominantly EU but a few jap and US releases of stuff that's not been released here), and even got hold of Powersaves 3ds to rip my private header to apply to the sky template.
I figured out Diskwriter in advance of the flashcart actually arriving, and loaded up the spare (Toshiba) 4gb sd card with half a dozen roms utilising my private header. One of the roms was Cubic Ninja, with the following rom on the card being Rhythm Tengoku The Best (Jap), so I could try out RegionFour (this was a few days before Ninjhax2 was released)...
The card arrived, I slapped in the sd, I went through the initiallising rigamarole... and everything worked fine. It cycled from rom to rom when the blue button was pressed. Everything loaded ok. Games saved fine. Cubic Ninja/RegionFour worked.
The only negative, in my experience, has been a problem with not being able to successfully back up .sav or .bks saves for non-eeprom saving titles (games that do save to eeprom are fine, and Diskwriter backs up and restores them without issue). It was kind of gutting to lose about 6hrs of progress on Pokemon Alpha Sapphire when I found the save file Diskwriter had previously created for it was only 1kb... but we live and learn... although I've still not found a solution to this issue, and have instead opted to just leave the couple of non-eeprom saving games I'm playing as the first two titles on the card and only delete/replace roms after them in the list.
Apart from this one issue, I couldn't be happier with my Sky3ds!