Just one thing to add really - if you get the high memory version (H) you can use the UTM features as well. You can get a month's trail licence from Juniper, so when you have practised everything else, book your exam (assuming you're going for the security track) and then activate your trial licence, and muck about with all the features.
When I did the JNCIS-SEC there were a LOT of questions about UTM, more than I was expecting (and probably one my my weakest areas, not having ever used it).
If you get the base memory version (B), you can pay to upgrade it (it physically has the same memory but you need a licence key to unlock the high memory features).
Oh and if you get the trial licence, pass your JNICS and want to keep going for the JNCIP or JNCIE, bear in mind you can't get another trail licence for a year. Its bound to the serial number of your device. So if you're feeling really good about things, when you do the UTM labbing, practice JNCIE topics! Should make the JNCIS easier...
Finally, let me know where you're getting one from! I really want a few SRX100s (was going to go for 2 B and one H) for a home lab.
Check this out too...
http://www.3fives.com/virtual-network-o ... nos-routerNot my blog but very handy.
Good luck!