To expand on that, the version you probably want if you have a modern setup (SLOT-1 flash card, possibly an expansion like the EZ-Flash 3-in-1 in SLOT-2), is the "No autoboot" build (flashme_noauto.nds). The version with "autoboot" will automatically boot from a flash cart in SLOT-2 on startup, which is a holdover from when the only setup was a PassMe tool and a SLOT-2 cart.
"No autoboot" is capable of doing this, but won't unless you hold the Select button. If you're fond of the health and safety warning or otherwise don't want people to know you flashed the firmware, the "stealth" version (flashme_stealth_noauto.nds) does everything else the same but keeps the warning.
I should clarify that the protection offered by FlashMe requires a SLOT-2 cart, as booting SLOT-2 is all it will do with a corrupted firmware. Basically, you'd put the FlashMe installer or uninstaller on a SLOT-2 device and flash the firmware again that way. If you don't have a SLOT-2 device and a way to flash it, you'll need to buy or borrow one if it comes to the point of your firmware being corrupted.
It's worth mentioning that after a certain point, Nintendo wizened up and made the entire firmware (barring user settings) read-only unless you're tripping SL1, so if your DS Lite was purchased in the last few years, the "protection" side isn't really something that FlashMe offers over stock hardware. Instead, it'll just be something that skips the health warning and can boot from SLOT-2 if you want it to.
As always, do note that there's a (reasonably small) risk of bricking when installing FlashMe. If your DS loses power before FlashMe has time to install its recovery code (this is the first thing it does), you'd need to remove the firmware ROM and flash it manually, which is probably outside the capabilities of the average user. You should weigh the benefits of FlashMe against your concerns of bricking your DS. If you take it seriously though and don't just carelessly ram a screwdriver in the back of the DS, you should be OK.
It's easier to trip the DS Lite and cause it to shut off by touching the wrong thing while you're tripping SL1, so it's advised that you take care in making a conductive tool conductive only at its tip. This means something like a piece of foil wrapped around the end of a toothpick, with electrical tape covering up all but the very end. There's no hard and fast rules for what to use. Last time I did it I didn't have any electrical tape around, so I foil-wrapped, paper-wrapped, then regular tape-wrapped a toothpick. In theory, an electrical-taped screwdriver should also do the job.
I'm making this sound more dangerous than it really is. As long as you're careful, you could do the job with any conductive tool, but it takes such little effort to grab some foil and tape that you might as well do it for the peace of mind. But as I say, if the reason you want FlashMe is to prevent bricking, it may not actually offer anything a newer DS Lite already has protection against.
