the downside I can think of is a lot of “idiom” depends upon who is saying it and context as to whether it is idiom or not, or it is being used in a specific way. Take a look at Urban Dictionary (a website)
trying to explain would likely send the Amazon Nannybot into apoplexy.
(note to moderators: as previously explained, the Amazon Nannybot is the daft algorithm that tries to censor rude words but just makes a mockery of what is being said (and it ignores idiom and linguistic difference) e.g. renders “hello” and “restart” as “***o” and “res****”)
if you can find an idioms dictionary that's formatted to work as a Kindle Dictionary, then yes, you can. There's an option to switch dictionaries on the fly when the definition comes up and I often use that to switch between a US and a UK dictionary. However most idioms are phrases and dictionaries only work on a single word. I've also found, that if you go to the full definition (on a Kindle) you will often see idiomatic uses of the word in the definition. I was puzzled by placcy in a UK mystery and it was in the UK dictionary.