The main distinguishing trait of the Ironfx is its diversity of accounts and probably the safety of the infrastructure.
Those are the features that stood out to me in the beginning and they were the reasons I joined this broker.
As for the downsides i would say that there are no downsides :)
Maybe except for the scarcity of the trading platforms. But it's quite subjective tbh.

Oh, you made me think of it.
I suppose that the main distinguishing trait of the ironfx broker - their account types selection which caters to the needs of a big variety of traders. Some like fixed spreads, others - floating. Some prefer stp/ecn execution, others - different type. As well as feel free to chose the acc which will be either spread-based or with commissions. Pretty versatile system, as to me.
The weakest? Hm... I presume the weakest one is the absence of cryptos for trading. Like, we are living in the modern world and still have no access to trading this asset =(