Daz, although it isn't 100% sure that apps on PlayStore will have no unwanted effects, Google do try to weed out the baddies. If you download and install apps from anywhere else, you might find it b*ggers up your tablet or costs you mucho money in telephone calls.
I can also recommend downloading Avast antivirus for Android and setting it to do a daily scan plus a scan of all new apps installed.....