What is this insect? And does it eat aphids on plants?
Based on the head morphology and the upper limb visible on the first picture, I would say it looks like a mantis. The length of the abdomen also confirms the same.



The internet is also full of several non-scientific sources that seem to confirm they eat aphids. Animals will normally learn to avoid bitterness in food as it's a sign of toxicity. I haven't found a lot of information about how bitter are aphids, however mantis are sit-and-wait predators, so they will try most things that crawl their way. Judging by the following pictures (and the article linked at the end), I would say it's very likely:





  Indeed, catching every prey would be a beneficial strategy because of uncertainty in encountering another prey due to a sit-and-wait strategy. By holding prey with its forelegs and gradually eating the prey by chipping away at it, the mantis has enough time to find edible parts of prey and reject unpalatable parts/prey (Reitze and Nentwig 1991).


Sources:


https://en.wikipedia.org/wiki/Mantis
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5882761/
https://praying-mantis.org/what-do-praying-mantis-eat/