A word of caution. I have no experience with them, but the PS-900 uses the third type of Metcal tip, where the coil isn't an integral part of of the tip but is a separate assembly whereas it is integrated into the tip with the other 455 kHz and 13.5MHz types. I don't know if this makes a difference to either heat delivery or ergonomics. It allows the tips to be manufactured more cheaply but whether that saving is fully passed on is another question. Most of the experience of Metcal around here (including mine) is based on the integrated coil type of tips used on the SP200 and MX500 series. It's quite likely the production irons with the non-integrated coil work just as well but it might be worth taking some soundings around here for someone with experience of them before pulling the trigger.
Edited to add: Oh, I see from another place that you've already pulled the trigger, guess that means that you can become the voice of experience on this. As blueskull says below, I believe you can use the handles from the integrated coil 470kHz tips on the PS900, so if it's pants you can swap to the tried and tested.
Edited to further add: Interesting, hadn't seen/noticed this before. If you're updating a post you don't get the "Someone else has replied..." warning, so I didn't see your new message as I updated this.