This little board works very well and is very flexible. It's great to finally have the Apple CD emulation for the picky Mac's that won't boot from any CD drive. Being able to mount hard drive images is cool too. You can read the SD card in a normal Mac/PC too and uses a config file (This is the preferred method, I'm not a fan of proprietary programs to manage this kind of thing). I have it in an external enclosure so I can use it with multiple Macs (especially with the CD emulation) as it's a fantastic recovery tool for any old world Mac.
Just to keep it balanced a little, I would say the only small complaint I have with it is the position of the SCSI connector. In the enclosure, and in some Macs the original short cable won't work. For my enclosure I ended up finding this monster 3ft long cable/connector set that's now stuffed in there. It's not a big deal by any means, but just be ready to get some slightly longer SCSI cables when you buy this if you have a really short one.
I've tried a number of alternatives to the MacSD, but none of them quite live up to what the MacSD can do. First, let me be clear, they all work. But which is easiest to configure and use? Hands-down the MacSD is the easiest to use, especially for modern Windows users. There's no special software required. It's simple. Put a SD card into your PC and copy a bunch of ISO, TOAST, and DSK files over to it. Then open a text editor, like Notepad, and create the config file. It's very simple, you give it the name of the disk image file and assign it a SCSI ID. Save the config file to the SD card, and you're ready to go.
There's no messing around with Linux-like commands. There's no clunky configuration app. There's no downloading software from github. If you have a modern PC or Mac and an SD card reader, you've got everything you need.
The killer feature that makes the MacSD better than the rest is the way it handles CD images (ISO and TOAST). You can put several of them on the SD card, and when in use on your classic Mac, it will mount the first CD image as if you had a CDROM drive. Drag that CD to the trash and it will auto-mount the next CD image on the SD card. You can have as many CD images as you have room for on the SD card, and it just rotates through them, starting at the beginning again when you eject the last CD.
The only down side of the MacSD is the configuration file. To be honest, it's a very small downside. If you're messing about with retro computers, you probably have a lot of experience with text-based config files. The config file is used to setup the SCSI IDs of the disk images and the order in which the CD images rotate through. It's not hard, and after looking at the example config that comes with the MacSD, you'll get the hang of it quickly. When compared to other SCSI-to-SD solutions, this config is super easy and very flexible.
Another killer feature that I have not had a chance to work with is that you can assign multiple disk image files as partitions under a single SCSI ID. So, you can have a TON of storage this way without interfering with your other SCSI devices. Lots of us have other things on the SCSI bus - like an internal HDD, a zip drive, a jaz drive, CD-ROM drive, etc. With only 7 SCSI IDs to work with, and a 2GB partition size limit (System 6 or 7), you can run out of IDs quickly. So, for example, you could have three 2GB partitions as a single drive and use only one SCSI ID. That's cool.
Overall, I highly recommend the MacSD to anyone who uses a Windows-based PC as their main modern computer but needs a SCSI storage solution for a classic Mac.