Does it matter?

Should I have reached a certain level before using it?

thanks

Which dlc?

For Lonesome Road, I'd say nothing less than 40.
It sound high, and it is. I entered at level 46-47 I believe and I got ultimately pooed on.( had it set on Very Hard though, that didn't last long)

Thinking of Honest Hearts & Dead Money

just to pop in and derail your thread slightly - are any of the dlcs expansions to the main quest, so I can complete the main quest without having to worry about the game ending?

^{For HH, I'd recommend going there from Lvl15 on and upwards.
Dead Money I'd rather not do before being at least Level 20, better 25. Also, being proficient in Energy Weapons and/or Melee is quite beneficial in Dead Money.}

Please don't say that, please tell me that was a joke?
To answer, NO! Obsidian worked hard on all the ending slides, they didn't do it so you could keep on playing. Playing a game once it has been beaten just takes away from the experience.

Now go and kill whoever you sided against and enjoy the end.
You can always just not beat it till your satisfied ya know.
This ain't skyrim-job nor is it Fallout:3, respect it, LOVE IT.
ENJOY!!!!

O.o Not proficient in either!

hey, chill out chap, I only just got the game, and was wondering how to play it. Does that mean I should play all the dlcs before finishing the main quest? Will some not be harder than the main quest itself? I'm just wondering the best order to do them in, and at what level (similar to op)

Yep, you finish the main quest, you finish the game, so definitely play the DLCs first. I've yet to go through the DLCs myself, but from what I've read I understand that there's a loose overarching narrative connecting the DLCs, and the order goes DM>OWB>HH>LR, if I'm not mistaken. Not sure what level you should approach each though.

You got Honest hearts and OWB mixed up.

I'd actually say that Unarmed is more important then Melee, but either/or when it comes to Guns or Energy Weapons. I've completed the DLC with both a Guns and an Energy Weapons character and I don't remember one being more difficult then the other.
In order of least to most difficult(in my opinion): Honest Hearts, Old World Blues, Lonesome Road, Dead Money. OP: I only put Dead Money as the hardest because it requires you to drastically change your playstyle which can be very difficult for some players, many people do consider Lonesome Road to be the hardest.

My personal order of completion: Honest Hearts, Old World Blues, Dead Money, Lonesome Road. I say this because I personally think the story works best this way. Honest Hearts is fairly easy and could be entered at about level 10-15 depending on difficulty. You should probably wait until about level 20-25 before going into Dead Money.

Thanks all for the info,

In Honest Hearts everything levels with you, so do that as early as you want. I completed it at level 9 without a problem.

For Dead Money I would suggest somewhere in the 20-30 range at the lowest. The lowest level that I've played through Dead Money was level 22, and it was still pretty difficult.