I am currently working at sainsburys in a gap year before heading off to uni. I work 20 hours a week on the checkouts.
I work two four hour shifts which do become hard because there is no break, the break entitlemenets at sainsburys are pretty good as most of them are paid breaks except dinner hours.
I think Sainsburys is an ok place to work however they are very very customer service orientated, i think they take this too far. Working on the checkouts a lot of emphasis is put on reaching the ipm (items per minute) target, however in my opinion customers dont want to be rushed through the checkouts, they want you to go at their pace not just chuck stuff through at them. Several members of checkout staff i know have had customers complain at customer services for going too fast. It does put us in a no win situation. If we go slow then the managers are on our back for not meeting targets, go fast and the customer complains.
Also you are expected to interact and make conversation with every customer, this is hard when some people simply dont want to speak to you.

Many times if the checkouts are quiet I have been sent to work on another department or to "dress" isles, basically tidy up, look busy. I dont think it is really fair because they send you onto other departments such as the fresh foods department and we become shelf stackers until they call us back, this is hard as checkout operatrs dont tend to know the procedures in other departments so end up constantly asking for help.

The pay I think is £5.40 for over 18s and £4.11 or something similar for u18s. I feel the over 18 pay is fair for working on checkouts as it is an easy job once you are used to it. However i dont know if it is worth it for little more than £4 an hour.

The staff mostly seem to get on well, although it is mainly checkout people seperate to fresh foods department and the gm section. Each department tends to stick with there own.

To conclude, in my opinion this job is ok as a temparary messure, however i dont think i could hack it as a permanant job, there seems little room for promotion and the job gets very boring.