I've got the original Teensy (AT90USB162). Aside from needing to get some digitally signed drivers so I could run it under Windows 7, it was very, very easy to flash.
I would hope the Teensy++ v2 is just as easy. It uses the same software that I used for mine, which is FLIP (you can get it off the ATMEL website).
60GB (120GB WD Scorpio Drive) PS3 (CECHA01, NTSC), 3.7OFW
60GB (640GB Samsung Drive) PS3 (CECHC04, PAL), Kmeaw 3.55, Repaired (Dead Laser)
PSP-1003 FAT, CFW5.00 M33-6 & Prometheus v2
X-Box 360 Xenon (JTAG'ed, 500GB HDD)