Coincidentally, I'm eating an RX bar for the first time right now! I've been trying a lot of protein bars, and these are the healthiest ones I've found. I wish the protein (12 grams) was a bit higher for the calories (200), but otherwise they're great.
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Some protein bars are little better than candy bars, with very high saturated fat from palm or palm kernel oil (e.g., the tasty Think! Boston Creme Pie bar has 8 grams).
The other issue is the sweetener. If they use sugar or equivalents (e.g., corn syrup), the calories tend to be high. Many years ago, when there were fewer protein bars, I used to eat Clif Bars, but they have only 10 grams of protein and a whopping four teaspoons of sugar (16 grams) in each bar, shooting the calories up to 250; I'll never go back to those. Several manufacturers use erythritol, which was thought to be harmless, but a recent study called that into question. I'm OK with stevia and/or monk fruit, two alternative sweeteners that (so far) have been found to be fine, but these are more prevalent in protein powders than protein bars.
I look forward to seeing more recommendations here...