The Harbinger and Dragon Eye expansions are a great way of accumulating miniatures for your roleplaying enjoyment. Don't expect any professional paint jobs using dry brush and ink techniques, and you'll be well pleased. For the price, this is the way to go to quickly enjoy miniatures battles.
For those that enjoy customizing/painting miniatures, these provide a suitable paint foundation to expand upon. Rather than having to start from the ground up as you would w/typical miniatures you buy for $5 a pop, you can quickly improve upon the look of the miniature through your own drybrush and inking techniques straight out of the box. Add ground cover and you've got a professional looking miniature that closely rivals lead-based.
Another advantage of using plastic miniatures is their ability to withstand being tossed around more during battle, or in storage. Paint on lead-based miniatures tend to chip more often due to their shear weight and inflexibility when colliding with other miniatures or objects.
The drawback w/plastic is that many long swords on these miniatures look more like melted taffy than strong and dangerous instruments of destruction.
Have fun!