Crush: Speed & Image Optimizer , 1,046 reviews

This app adds 13 random characters to the picture name. This forces the user to manually look up the picture name every time. In addition, this number detracts from the picture's SEO. If it wasn't for this added number the app would be more useful to us and my review would be more positive.

Pro: it only allows you to optimize to a certain point so that your pictures should still look great.
Con: The interface+process needs work and you're charged via file size. And if you try out all 3 modes of optimizing then you're charged 3x for the same 1MB picture.

Doesn't work with our image.

We wanted to make sure the compression algorithm for lossless was powerful enough (30% announced sounds quite low in comparison to tools like TinyPng), so we ran a trial on one specific product.
We optimized all images, lossless at first, then a few with lossy compression.

The app says xx% compression, but Google Page Speed says nothing changed.
Ok, we downloaded the so said "compressed" images, from Shopify (changing the ?variable to make sure we have the latest version)... Nothing changed.
So, let's try to download the preview image displayed on screen that is supposed to show a comparison between the old and the new image.
Surprise... Same image, same size.

The comparison tool is very fancy, but both images are not on the same layer, the second image has a small offset of a few pixels, so it gives the impression the image is not identical, but it is.

Again, it might just be a bug, but the fact the tool says the image was compressed by "xx%", and that the comparison tool second image is offset a bit is not reassuring.

Edit:
I'm suspending my judgment temporarily. We've been in touch with the developers and it looks like our image are already too optimized for their app to have any significant effect on one hand, and that Shopify is messing up with optimized images (increasing their size) on its end.

For now, my first conclusion is that this app is pointless for those who know how to save their images (photoshop, gimp, or recompressed with online tools like TinyPNG) because Shopify already has its own algorithm.
Since Shopify algorythm increase the size of overoptimized images, negating the benefit of this app, it sounds pointless.
See here about image compression issues with Shopify: https://ecommerce.shopify.com/c/ecommerce-discussion/t/shopify-image-quality-optimization-round-2-with-stats-38-improvement-304813

We're in touch with the developpers, if something come up, I'll update my review;
Until then: I do not recommend the app to merchants already saving their images for internet use with proper comrpession.

I installed the app on my shopify store, but after I tried to open it the only thing I see is a blank white page. I don't think it works

Not impressed. It counts the size of your entire image towards the quota, not just how much it saved. If my images were already all optimized, I'd run out of bandwidth, even though I shouldn't, because there's nothing to optimize.