A number of years back, I was trying to make a decision between getting a wireless mic and a monitor, and went with the monitor. The monitor I ended up with was the TC Helicon VoiceSolo 300XT, and it has served me well (unfortunately, it's no longer made). The Roland that you have is one I have more often seen used by keyboard players as an aux monitor, and I don't believe it has any way to place it on the floor or on a stand where it is angled up towards you, which is a feature I would look for in any callers monitor. It's possible you could rig up a stand that would allow you to tip the roland back, or possibly get or make an angled mount that would let you tip it back on a mic stand. I believe that it is capable of all of the other things I would want to see in a monitor besides that.
Other features that I would be looking for:
- a "thru" connection for XLR, allowing you to plug your mic into the monitor, and then send a feed to the board, and where the adjustments made on the monitor do not affect the signal sent to the board.
- A way to mount the monitor on a mic stand, which gets it up closer to your ears
- The possibility of taking a monitor feed from the board if you do want to be able to hear the band in the monitor (particularly nice for singing squares, or for larger bands where you can't hear the folks on the far side of the stage.
I really like having a monitor for the reasons John mentioned: it make it easier to balance your volume with the band, and less likely to abuse your voice because you can't hear yourself. John is also correct that hearing yourself in the monitor is no guarantee of good sound in the house. So I also have a wireless mic and if I am not confident in the skill of the person running sound will generally go wander around a bit during an early dance to see what it sounds like.
Jack