Sometimes I get asked about custom harmonicas. What makes them custom? Will they help me play better? Do I need one? and so on.
Happily, Lee Sankey has made a video which covers just about all the points you should consider. The only thing I would add – Lee talks about the advantages being mainly for the player rather than the listener. He’s correct of course but it’s important to also consider how playing a very responsive and comfortable instrument can encourage and inspire you. The audience will definitely notice the difference between a performance where the player is comfortable and confident, and one in which she’s fighting a sub-standard instrument.
That said, and as Lee notes, off-the-shelf harps are really very good these days and you do indeed need to be very unlucky to get one that can’t be bought to life with just a little attention (DIY harp setup is a whole other subject for a different day).
Here’s Lee’s video. Much wisdom therein.