RonMicjan

there are several answers to how deep and how long

How Long?
duration of the scrubber canister used, there are more than one version for many rebreathers, 2 hours up to over 10
duration of your oxygen and diluent supply, a 13 cf cylinder can last me for 3-4 hours.
bottom time based on decompression status, how much Nitrogen and or HE your body has absorbed, before you have to make stops on the way up, or how long of stops if you continue into planned deco diving. An 80 foot dive for 120 minutes at 1.2 setpoint will obligate you to 10 minutes of decompression. Most folks will not be able to get an alum 80 to last that long at depth.
thermal considerations, in warm water a person can stay under for many hours, in cold water, it is based on how cold and what kind of thermal protection you have. My longest cold water dive is around 2 hours, warm water dives have run into 3, by then Im hungry...

How deep is mostly based on your level of training and comfort. different machines are rated to different depths. Cedric did his 600+ on a meg (my chosen weapon), his partner was on an ouroboros, AP machines are rated by CE to 300ish, the manufacturer now says 500, CK is 250ish and the SK is 165. What kind of diving do you wish to do? Pick the correct machine now and it can take you a lifetime to outgrow it, or pick the wrong one and outgrow it in 6 months.

Advantages over normal open circuit scuba are relative, gas efficiency can be as high as 100 times greater, depending on the depth you compare at, cost is significantly higher to get into the game, (unit + training = 5500-15,000)but savings while diving using helium based mixtures can pay for your CCR eventually. Instructional costs are higher, consumables (scrubber material) can cost more than gas fills for OC, but one can run to 10+ hours on a $20 scrubber fill.

you are in the right place, keep reading and learning. Hit some of the articles, but remember, what someone's opinion is, may not match what you want to do. most everyone will swear that what they dive is the best and all the rest are cattle patties. This is especially true for someone who is selling brand X, but not brand Y, consider the source. Advanced diver magazine occasionally sets up Rebreather tryout days in a pool, check into one and good luck.

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