I use an Xkey 25 (USB, not bluetooth). It’s really portable for travel. The 25 keys a just a skosh small, it seems. I have to switch octaves frequently for the type of music I’m entering. Sometimes I just want to play chords or multiple voices with note entry turned off, to see what the music sounds like, and that’s where I run off the ends a lot.
I don’t travel much, so a 37 might be my sweet spot, but haven’t tried one.
Most MIDI keyboards use USB cables direct to the computer these days, if that’s what you mean. Only serious kit still uses the 5-pin DIN cables. (And now there’s even MIDI by Bluetooth!)
But yes: the Roland A-49 is only connected by the USB cable (which also powers it!) to my computer.
Interesting that it transfers midi on both midi in/out and usb.
Oh yeah – it does have a 5-pin DIN out as well! 
Forgot about that.
I like my Korg MicroKEY Air 61 for these reasons:
Is the bluetooth reliable? Assuming i woukd not gave an issue with my macs. I’m torn between roland A49 and the Korg microKEY 37. Im willing to try bluetooth though
Solid for me unless I take it far away.