I know how the SSG-550M series can be loading with Junos. At the end of the day whats the difference between an SSG-550M running Junos and an SRX device. UTM features aside.
Is there any known issues or performance looses with doing this?
Not really. The main difference you'll see if that the J-series boxes are single-core processors while SRX branch products are multi-core. Since the J's and SRX's are processor-based boxes rather than ASIC-based (processor-based gives lower performance than ASICS, but with much greater flexibility and at lower cost), you'll notice that the J-series will max out much faster than SRX; if you're not pushing the box to its limits, then they'll behave mostly the same.
