Jobslinger I find mostly is a useful tool for new shoppers to find companies they know to be shopping their area. I figure there is no point in signing up for 50-100 companies until you have at least a few shops under your belt and know that it works for you and your work is acceptable to the companies. Very few shoppers 'survive' more than 6 months and it is of dubious merit for them to sign up with lots of companies before they know if this works for them. And although most folks promote signing up with everything you can, I really think a more measured approach makes more sense. You know from every forum that outfits such as Market Force and Corporate Research International and Maritz have shops in virtually every community across the country. While these are not good paying jobs, the reality is that a newbie is not likely to land good paying jobs right off the bat, so they are 'get your feet wet shops'. They have the advantage of being beginner friendly companies, providing training that for newbies is pretty complete but for experienced shoppers chafes as a waste of time and energy because it is what we do automatically all the time, every time, anyway.
I do check Jobslinger about once a month to see if there are any companies I am signed up with who now have clients in my area I did not know about. I have never found a new-to-me company on Jobslinger.
I have an excel spreadsheet of companies I have heard about on forums but have not had an opportunity to explore thoroughly. On occasion I Google various terms that may elicit some listing of companies and I collect their data to my spreadsheet. Be aware that Google changes its search algorithms frequently to avoid having folks game the system, so the selection you get returned for a specific search is likely to be different in a month or so from what you find today. I have had lists pop up with companies whose last copyright date was 1997 and with no sign of current activity. Most of the time you can't tell how old the list is except by having watched 5 years ago as this company went belly up and that company was bought out/merged with another company three years ago.
Over the years I have acquired a network of shoppers with whom I PM and email and if I see a job in Suzy's area I may ask her if she is signed up with XYZ because they have a nice shop near her. Suzy generally does the same for me and since some companies I never signed up with because they were adamantly regional (and not in my region), it may be a lead on a company I never heard of before or that I never bothered with because they only shopped Outer Mongolia.
The trick here is to keep your eyes and ears open. Keep a good list of who you ARE signed up with because with many/most of them if you don't visit their website within 3-6 months you may well find that you have been dropped from their shopper database but can't sign up again because that SS# is already in use by your dropped/expired self. I make it a point to go to the profiles and change something to refresh it--since in any 3-6 month period my weight has probably gone up or down by 5# that is a simple enough change to refresh the profile if everything else has stayed the same.