First time buying bipod

Never used a bipod before. Always use a bag or something to lay the gun on top and shoot. So deciding to get a bipod and try it out. What's a good length or standard for bipod? I see them on Ebay like 6 to 8in. 7 to 9in. 15 to 23 in..etc. not sure what is the standard for bipod. Plan to use it on an fx impact so which length do I get? I dont want it too short or too long. 
 
I got the clone of the Atlas for my ImpactX off eBay. It is very well built, cheap enough to experiment with, and easily changes lengths to suit your height requirements. One other nice feature of this is that it pans and tilts so you can keep the gun level without having to fiddle around with adjusting the lengths of each of the legs individually.
 
Just make sure you get one with 45 degree leg (5 position settings) For instance the Magpul one is awesome and priced so right...but it will put the gun up so hi on you and 45 is more stable anyhow. I opted to spend the big money on nice guns, and continue that trend spending good money on a nice Atlas bipod. Plenty like the clones though and if your just testing the waters it could be a good idea, plenty here will line up to buy one used
 
What's your budget because they are some awesome bipods north of $300-$400? I have an old 90's model Harris Bipod, a newer Harris with cant adjustment, an Atlas PSR BT46-LW17 and a new Accu-Tac BR-4 G2. For something light weight, the Atlas works great. The only thing I don't care for is that the cant/tilt doesn't work so well. Not sure if I got a defective unit or not. The Accu-Tac BR-4 G2 is awesome. 

No pan/swivel but I don't care to have it. The cant/tilt on the BR-4 is a lot smoother than the Atlas and it can be locked in tight with the lever compared to the Atlas. The BR-4 and pretty much the whole line of Accu-Tac bipods feel bomb proof but it comes at an expense of weight. It is a lot heavier than the Atlas bipod I have. I decided to keep my Atlas because it fits very well with my Edgun Leshiy as a complete package. If I was only allowed to keep one, it would be the Accu-Tac BR-4 G2.