I found this at a thrift store for four US dollars and it's been my main MIDI thing ever since. No problems with SysEx, no crashing, no latency, no bad drivers, just a smooth experience on macOS 10.14. The only frustrating part is you need to get drivers tucked away on M-Audio's site - they don't CLAIM to support it anymore but the Anniversary Drivers work great. https://m-audio.com/support/download/drivers/midi-usb-driver-v3.5.3-mac1
I'll be sad if they ever, truly take support away. This thing is cute, small, reliable, and well worth the $40 on the used market.
Will report on functionality and use once I bring it back into the fold, now that I have found and installed the drivers I previously believed was non-existent. They can be located here: https://goo.gl/7CYMFH Drivers can be used for a host of Legacy M-Audio MIDI I/O devices.
The MIDISPORT USB MIDI Interface has the following features: • MIDISPORT 1x1: 1-In, 1-Out MIDI Interface (16x16 MIDI channels) • MIDISPORT 2x2: 2-In, 2-Out MIDI Interface (32x32 MIDI channels) • MIDISPORT 2x4: 2-In, 4-Out MIDI Interface (32x64 MIDI channels) • MIDISPORT 4x4: 4-In, 4-Out MIDI Interface (64x64 MIDI channels) • High-speed connection to USB-equipped PC or Apple computers • Windows XP, 2000, Me, and 98 —true Plug and Play compatible installation requires no IRQ, I/O Address or DMA channel setup • Macintosh installation requires OS 9.2.2 or higher, OMS required for 9.2.2 only • "MIDI Thru" push-button allows you to play your gear even when your computer is turned off, without having to disconnect cables (MIDISPORT 2x2 and 2x4 only) • MIDI-In and MIDI-Out activity indicators for each port • Self-powered—requires no external power supply