Hi, I've done programming with the Symbol .NET SDK. I think it works okay (unlike their old control for eVB which was unusable).
As for the MicroFlash printers, we've used an IrDA model. I think O'Neil is the OEM for Symbol on these printers, and ours are original O'Neil branded.
The printers are kind of finicky about receiving data, or at least, ours was on IrDA. If I send data to them too fast they just lose data, but there's no handshaking (I don't think) so you have to send slower than you should be able to.
Printing images was a pain for us too, I had to write some custom C code that converts a .BMP to what the printer understands, with compression.