I use the Mackie SRM150's (a pair) for monitoring. They are loud enough to keep up with a full bore live band, which no built in speakers ever will be, and offer considerable flexibility with connectivity (a lot more than most built-ins).
Sure, it's a bit more to set up, but the sound is great, and I rarely play gigs that are so quiet the built-ins would suffice.
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An arranger is just a tool. What matters is what you build with it..!