I find ISS to be buggy as hell... about half the time their app lists shops but you cannot assign them as they constantly tell you to "pick another date" -- even if I go through all the possible dates the message pops up and I just wasted time. I only keep ISS around for NWLPC which is a local company and has a number of clients here, as well as BMA which posts the occasional cell phone shop which can be a nice little filler.
Personally I've found JobSlinger+ to be worth it's weight in gold... it's $18 quarterly to subscribe -- but allows you to manage all the Sassie companies in one place -- and I'd say the vast majority of companies with shops here are on Sassie. The situation may be different regionally, but if I had found ISS before JobSlinger when I first got into MS'ing, I'd have probably felt like I couldn't make a serious side income doing this and got dejected... ISS is good for fill jobs... but it seems like JobSlinger (when you properly fill it up with Sassie companies) is where most jobs are-- I've also found that companies who use ISS don't seem to pay as well as those who use Sassie. That may be a coincidence, but I know which platform 85-90% of my work comes from...
There's also GigSpot which is for ShopMetrics clients -- but it's a similar situation... only a few jobs here and there, and they don't seem to pay well... Ipsos and Coyle who are on ShopMetrics and have a number of jobs here aren't on GigSpot so I find I have to log into their sites manually to look for jobs.
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