The inexpensive smartphone slide scanner (actually a digitizer) just arrived. My very old PrimeFilm
That scanner produces much better copies, but, it's drivers no longer work with my windows 8 & 10 computers. However, in my opinion, for $30 this is a pretty good solution. My android phone (a Moto G6) had a couple of issues that I had to address first.

The distance from the phone's lens to the slide is too close to focus the Moto , but I was able to address that by putting a half inch spacer to move the phone slightly further away from the slide.

It was necessary to use the the Moto's manual camera controls to get acceptable copies. The Moto's manual controls include manual focus and exposure and the camera also provides manual "zooming" to frame the slide image. (note that "zooming" a digital image reduces the image resolution)

I assume that the device is designed for iPhone, but it is a shame that the designer didn't put a little more time working with android phones.

The big issue is lens distance and it would have been dead simple to include half inch posts to extend the support rods.
The hole for the lens doesn't fit the Moto.
The slide holder doesn't fit metal slides.
The illumination background is rectangular, so, it won't work with square slides.

Also, I DID NOT use the app that the scanner provides... For the testing, I simply took the images which were uploaded to google photos, went into google photos and cropped them to fit.

Any good image software such as IrfanView will allow using the scanner to take a large number of images, then use batch processing such as rotation to fix multiple images at once. You can also scan 35mm negatives and mass convert them to positive using IrfanView.

I like this device. It was a very good value for the price. I was able to digitize a lot of old negatives and slides, so I can pick and choose which to have developed professionally. It was a little tricky with the slides, as some of them were a little tight in the holder, and there was a potential for bending of the film.

I used it with an iphone 7, with acceptable results. I have recently upgraded to a Samsung S21+, and I'll be re-digitizing with the new phone. I will update the review with the results from the new phone camera, which I anticipate will be an improvement. I recommend this device.

Make no mistake, this is a plastic elevated platform for your smartphone to take zoomed in photos of old slides using an LED backlight. Your photos will only be as good as your phone's camera, editing apps, and your own editing/photography skills. That being said, if you have some degree of photo editing knowledge and a decent phone you'll be pleasantly surprised by the results! For the price, it beats mailing your slides out to some service to have them professionally scanned costing hundreds. If you've got a box of slides catching dust and some time on your hands because of COVID related lockdowns, this is the tool for you :)

Couldn't be happier with the results. Most of the work is done by the camera on the smart phone, but the simplicity and the low cost make this purchase a no brainer for digitizing old slides

I have a collection of 35 mm slides I have been wanting to digitalize. This scanner fits the bill. Easy to use. Just turn on the light. Put the phone camera on top and use the application to scan and make all the necessary adjustments. I have an iPhone 12 which has no problems focusing on the image. The resolution is not the best but that's expected for this type of scanner. I find the image adjustments adequate but tint and sharpness adjustments are better on the iPhone.