Grouped Products Filter is a highly useful function that allows the user to use drop down menus to filter the list of grouped products by attribute. For example, if you have a t-shirt grouped product that is available in sizes Small, Medium, and Large, a drop down menu will be automatically created above your grouped product box. When the customer selects Large from the drop-down menu above the grouped product box, then the "Small" and "Medium" products will vanish. This will work with as many attributes as you would like. So if the products have a choice of color, size, shape, material, or whatever, these can all be used for filters as well. This is extremely helpful when your grouped product has many children.
The extension is also intelligent enough to know when to not create a filter. If all products in the list have the same attribute value, a drop down will not be created for that attribute. For example, if all of the t-shirts come only in red, a drop down filter for color will not be created as it is unnecessary.
Grouped Products Filter went through a major update that now remembers layered navigation settings! When a user is browsing a category or search results page and they narrow their selection using layered navigation and then click into a product page, the grouped products list will be pre-filtered according to their layered navigation selections. This is not only convenient, but it takes some of the confusion out of it when a customer is presented with a list of grouped products and doesn't know which one is the right choice for them.
Additionally, the most recent update significantly reduced the code base needed to run the extension which makes it faster and less intrusive. The old version of the extension used to contain a template file for the grouped products list which you needed to use. Now, that is no longer necessary! It will automatically work with either Magento's default grouped product list template file or any custom one that you have already set up.
The extension also includes a convenience feature which allows you to decide the order in which your products are displayed within the grouped product box. You can sort by "Magento's Default Sort Order", "Name", "SKU", or "Price" and you choose to sort in ascending or descending order.
One of the best aspects of this extension is that it works with both SELECT and MULTISELECT Attributes, unlike configurable products which only work with "select" type attributes. Additionally, Grouped Products are easier to manage in the backend than configurable products in general.