There's been a few threads on those, be carefull! They can bite you and your cham so I would definitely cup feed, only giving a few at a time. If you do a search you will see a couple of people that have been bitten, looks like it hurts!
Yes.
The black Gryllus bimaculatus aka two spotted ones are bigger (than Acheta domesticus, the brown ones) and they have a more noticable bite (either type can bite and should not be left in the cage uneaten) and they are louder as adults. They are easily gutloaded and make a good feeder.