IOTA at the time of writing is user-unfriendly, unproven and perhaps fundamentally unscalable.
Most alarming is how the development team reacted to a cryptographic vulnerability found in one of their self-made hashing functions. The IOTA team dishonestly said that it was an intentional flaw before patching said flaw and subsequently suggested that there could be more intentional flaws. Another instance of dishonesty was the IOTA team exaggerating their partnership with Microsoft and other big-name tech companies.
While interacting with people on their subreddit the IOTA team is rude and abrasive.
Below are links to articles that describe some of what I mentioned and other common issues with IOTA that I haven't mentioned.
https://www.media.mit.edu/posts/iota-response/
https://hackernoon.com/why-i-find-iota-deeply-alarming-934f1908194b
https://shitcoin.com/iota-cannot-be-used-for-iot-loss-of-funds-may-occur-e45b1ed9dd6b