I guess I'm qualified to answer the questions as I'm currently locked into a CB6000
First, the only BAD thing I've come across is the possibility of the two halves of the sheath coming apart along the weld line. This is undoubtedly a problem with the fake CBs, I did a just-in-case and ran a very small bead of thin superglue along mine (which is a "real" CB6000)
You need to choose which of the two lengths to buy. Until I started getting interested in chastity play, (PLAY ????) I didn't even realise that male population is split into "showers" - whose penis is much the same length flaccid and erect, and "growers" - you can guess what that means
As the intention is to stop erections, if you are a "grower" like me, then get the CB6000S, a "shower" the CB6000.
You need to play around with the rings and spacers to get the correct fit (the box contains various sizes) The ring needs to be big enough to allow good blood flow (!) but not so big the whole lot drops off. The spacers set the gap that keeps your balls outside the ring/sheath, again to stop it dropping off. Also, if too loose, you can apparently (I never have) get your penis back out of the sheath, though getting it back in would be very tricky. It is in your interests to get this right.
Apart from one occasion when just one ball got through the gap (very painful, the result of some over-enthusiastic crouching on the floor at work 90 miles from home and a key), mine has been completely effective and secure. I wear it as part of our ongoing and developing D/s relationship, when LadyJ thinks I should. This may be as a minor punishment, for a few hours, or if we are going to be apart for several days, or if she feels I need reminding who is in charge ( the longest so far is two weeks).
The psychology of it is interesting. For me, it puts me in a submissive frame of mind, which can be to her advantage in that she gets things done that might otherwise be put off. As I never know how long the lock-up will last, it is a strange mixture of excitement (the CB provides a constant reminder of sex, or the lack of it , giving a low level of stimulation) and trepidation, as there is also some mild discomfort - occasional unexpected pressure or tension as you move around, though you soon learn what to avoid. There is also the necessity to pee sitting down, which can be inconvenient when you are used to being able to pee anywhere vaguely private. Some see this as humiliating, personally I don't.
On a practical basis, you need to be released to clean both the CB and yourself. I am unlocked for enough time to do this, then I re-fit the CB and present myself for inspection with the lock clicked shut. I use simple soap-and-water for cleaning. You will almost certainly need to lubricate the ring and sheath, otherwise you can get a nasty burning sensation when things get a bit tight as you move around. I use Johnsons Baby Gel, which lasts for the 24 hours between cleaning.
And then you come to the consequences.
Night-time erections can be very uncomfortable. Some find them extremely so. I found that my body got used to the situation very quickly, and any erection subsides before it gets uncomfortable - nothing's going to work so why waste the effort! However, if your Lady decides to deliberately get you excited, then she can have a lot of fun watching you desperately try to avoid an erection, and tease you knowing that it is all in vain as far as you are concerned. As happened to me last night, your Lady might order you to pleasure her in any way she chooses, whilst you are merely the "mechanic" who provides the stimulation without being able to join in or gain any satisfaction yourself, except the act of giving her pleasure. This is both exciting and frustrating, but also acts as a strong reminder of who is the Dominant.
There is a lot of fantasy about chastity. The reality is that you really are putting someone else in control of your sexual activity. A sub friend of ours is locked in his whenever he is away from his Domme, not that she distrusts him, it is simply part of the D/s relationship that she has full control of all of his sexual activity. If based on a loving relationship, it can add greatly to the excitement and intimacy to be experienced, and if you are exploring the D/s style of relationship, it is a valuable tool. But as timeupalso has said, be careful what you wish for, you may be releasing the genie from the bottle by offering yourself into chastity!