Built in CMS is nice so you don't have to purchase a separate product. The Insite code is .C# and ASP.NET based which is good if that's what your expertise is. You can purchase the API functionality which allows you access to build along side and customize some of the Insite functionality.
What do you dislike?
Be cautious of their sales team. They promised things they can't deliver on out of the box and downplayed difficulty of customization. Product was designed for off the self experience, period. The base code is changing fast and makes upgrading a major nightmare if you customize. Insite doesn't want to deal with it's customers directly. They seem more interested in growth for their equity partner and future sale to competitor than long-term growth for their customers. You'll be pushed off onto third party partner. The issue is that their partners are limited and have limited experience with Insite code. Most partners are geared toward Sitecore and have serious challenges with any custom implementation. Expect your partners to underestimate everything,, timelines to be five times the original estimate, implementation costs to be five times original estimates. In truth, if you need a customized solution, I'd stay away from Insite. For pay, SAP Hybris is much more flexible and you can negotiate the price down to about two times Insite. While this is initially more expensive, it will save you in the long haul. For free, there's nopCommerce, been around a long time and support costs are an absolute bargain compared to Hybris and Insite.
Recommendations to others considering the product
Strongly encourage you to look at other vendors if you are going to do any customization.
What business problems are you solving with the product? What benefits have you realized?
Replace an old E-commerce product. We haven't realized any benefit. Everything we have we had in the old product.
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