The BitFlyer app seems to be a good alternative with no commissions and a lower fee structure than Binance. The company is headquartered in Japan and operates on the EU market from Luxembourg. In my opinion, their site is clean and simple, since they don't offer a lot of coins and tools.
Could anyone tell me more about this exchange? What is their legitimacy? What kind of experiences have you had?
What is your reason for using this platform? Do you mean avoid KYC because I think you must pass KYC test for using BitFlyer and IRS will know all of your transaction due to the many relations between Japan and the United States.
On the safety side, the platform is a private company registered in Japan and has its headquarters. It is safer than Binance, but I do not think that you will find all the trading pairs with the liquidity you want on Binance.
If you do not have a problem with identity verification and want to trade, Binance is better, but if you are looking for main pairs, BitFlyer is better.