Seems about right, and remember this is total throughput, so full duplex is 250 Mbps each direction. Juniper recommends a 340 if you want to push 1Gbps full duplex.
I've found Juniper to be fairly accurate in terms of throughput numbers.
I'm not sure if you can subscribe for feeds or not via someone like CDW. I've never tried. I have purchased licenses for used gear with Juniper without an issue. For the JSB for example you have to enter the serial of the device on Juniper's site, but then it entitles it, no questions asked.
We've purchased a few used Juniper items on eBay and licensed them. If you're careful you can even purchase support. You need a valid support contract to purchase the IDS things.
Alternatively you can toss these things into packet mode and they're reliable 1Gbps routers, totally silent.