For over 5 years now, I've managed an E-commerce site with over 3,000 products and 40 Plugins and heavy traffic. We installed the IS+ plugin and signed up for premier service since day 1. This is by far the most important and valuable plugin that we have added to our site. Not only it has incredible search functionality, but also it handles our product category pages, Navigation, Product Filters, Recommendation Engine, and Recently viewed products and much more. Pretty much all of our front end product search functionalities are being handled by IS+ for the last several years.
The system is easy to use and super fast. Loading time has always been excellent, and so much of the load from product queries are done on the IS+ server which frees up our server to handle other functions. Also, their system is continuously being improved and new features are added every few months. The interface is easy to use and very customizable.
Most important of all, knowing that we are relying on a plugin to handle so much of our site's functionality, Great Customer Service is extremely critical. And IS+ support has been outstanding with prompt responses and support team that will stick with us to solve any issue or update we need.
I think if you are ready to step up your e-commerce site to the modern and future level, then you should not hesitate to give this plugin a try.