The make up of the DOD FX40 Graphic EQ is extremely easy to follow and has an overall very high level in terms of ease of use. It simply has six bands and another slider for overall level. The frequency bands are each fixed at frequencies that pertain to guitar, including 100 Hz, 200 Hz, 400 Hz, 800 Hz, 1600 Hz, and 3200 Hz. Each slider gives you the ability to cut or boost 18 dB above or below, which is more than enough needed to get the job done. The manual for the DOD FX40 Graphic EQ isn't a necessary to have and I can't speak to how helpful it is or not as I've never seen it.
The sound quality of the DOD FX40 Graphic EQ isn't all that great in my opinion. While it certainly is possible to boost your guitar level with this pedal, as far as using it as a traditional EQ goes, it is pretty limited in its use. The frequencies are fixed at good positions for the most part, but I'd rather have the ability to choose my own. It also seems to color your tone, and not in a good way. It feels like it cuts out some of the signal and certainly isn't true bypass by any stretch as well, meaning that even when it is not engaged it will take away a bit from your sound. I've only used this pedal with electric guitar, but would work just the same for acoustic guitar or keyboards. I wouldn't use this for bass guitar as the fixed frequencies don't translate.
I first used the DOD FX40 Graphic EQ about two years ago and can't say I would recommend it to anyone as I'm not a fan of the sound quality at all. It colors your sound and takes away more than it will give you. Although it is cheap don't be fooled as it isn't worth any amount of money. Do not waste your time with this pedal as there are plenty of other EQ pedals out there for reasonable prices that sound way better.