I have used both the Griffin iMate and the cheap (~$5) Arduino Pro Micro solution. Both work fine, but if you are handy with electronics, I would recommend going the DIY route, because it is equally functional to most other converters and also way cheaper. (a four-pack of Arduino Pro Micros costs only $20)
I have an Apple Extended Keyboard connected to my modern iMac using the iMate adapter. Some quirks are that the caps lock key has never worked under macOS (except for some reason in Bootcamp it does) and that I have no ability to control functions such as volume using the keyboard (at least without installing some keylogger software, which is a cybersecurity no-no). Otherwise, it works fine, and I have used this as my main computer keyboard for years. In fact, I am typing this post with it right now.
My Arduino Pro Micro converter is wired up to an Apple Extended Keyboard II and another modern iMac. I have hidden the Arduino PCB inside the keyboard, so it looks fairly stock, with the exception of a USB lead trailing out of it. I installed the QMK firmware on my Arduino, and I have programmed it to have more functionality than my iMate keyboard does. Caps lock works with this keyboard, and I was able to set up a layering system so that I can use the F10, F11, and F12 keys to either act as function keys or control volume depending on whether I am holding down a modifier key. I prefer this Arduino converter to the current commercial options both because it is way cheaper while offering the same functionality (excluding the wombat which can do more things than most converters). If I wanted to, I could easily build my converter into an external enclosure, and I wouldn't need to physically modify any of the keyboards.
Open-source keyboard firmware for Atmel AVR and Arm USB families - qmk/qmk_firmware
github.com
Both converters also support ADB mice, and if I wanted to have a left-click-only computer for some reason, I could use my Macintosh ADB mouse with my modern iMacs as well.