Pionex is a real exchange with a real track record. It has operated since 2019 from Singapore, lists more than 400 coins, and runs bots that hundreds of thousands of people use daily. For Americans the relevant entity is Pionex.US, which states it registered with FinCEN as a money services business in April 2020 and has since obtained money transmitter licenses in a number of states. That is a stronger U.S. footing than most offshore exchanges can claim.
The doubts in public reviews are about process rather than theft. Customers describe withdrawals blocked for a "security concern" until a higher KYC level clears, accounts frozen for "high risk transactions" with no timeline, and KYC rejected repeatedly with the same generic email. Pionex responds to these reviews and says it aims to clear withdrawal issues within 24 hours, but the volume of complaints is high for an exchange its size and the Trustpilot score sits around 2.5 out of 5.
The honest read is that Pionex is legitimate and custodial, which means your ability to get your coins out depends on its compliance team's mood on the day. That is the normal texture of a centralized exchange, and it is exactly the situation where a company with a phone number, a branch, and a non-custodial wallet on the other end of the trade is easier to deal with.