WhimSpin

Came searching for an app to group products together, and found OPTIS. Not only does it group products, but it also provides multiple options for variant selection display, ability to display variants on collection pages, a very intuitive configuration and setup UI, and remarkably responsive support through their built-in chat. One thing I'd like to see added - they currently rely on Shopify's default variant availability. I.E. - size can be marked as unavailable for a particular color, but it doesn't reciprocate to show unavailable colors for a given size. Given how responsive they've been to-date, I have confidence they'll address this very soon.

Have just started using the app, but so far is really easy to use, straight forward in features and pricing, and has excellent support. Only reason for 4 stars is the price-point. It's a little pricey for me at the moment.

It does one thing, and does that thing super conveniently, working in the background once applied to your theme & embedded on your product page. After that, you set everything up intuitively from the native Shopify product settings pages. I was a little slow to get started, but super easy once I figured out a couple nuances about Shopify's product configuration pages (like how to see all the images associated with a particular product). !!!Note!!! - if you use Printify (or likely any other dropship/POD supplier) and sync images from their apps, you'll likely need to repeat the organization steps each time you sync/publish the media from the other site as it will re-arrange the order of the media associated with your product.