jtag and rgh consoles are the same thing functionality wise . they are essentially a homemade xdk (xbox 360 devkit), jtag is only for the original phat 360 and based on a software exploit in the hypervisor due to a bug in a old bootloader from 4532 to 7371 , the only difference imho is that a jtag is always instaboot ( it boots in the same time a stock console would), rgh is compatible with all hdmi consoles including slims before 2014 ( non hdmi is possible but not reliable) above 7371 but is based on a hardware exploit so boot times can range from instaboot to several minutes, rgh allows your console to downgrade to a modified 4532 kernel to use the the old hypervisor to allow unsigned code.
jtag, rgh, and devkits are the consoles most commonly used to host modded lobbies online, run emulators and homebrew, a flash dvd drive ONLY allows burned dvd-DL to boot, does not allow homebrew or any custom code, only dvd rips
there is a small learning curve, pretty much xexmenu or freestyledash, you can either copy from usb drive (imho easiest and quickest), ftp (can be slow), xbox 360 memory cards (remember those?), or browse/rip dvd's to the hdd, you do not need a flashed drive with an rgh/jtag xexmenu and fsd can read burned disks, think of jtag and rgh as a way to convert the xbox from a game console to a personal computer