Keep in mind, this is IMO.
<Flame suit on>
I hated my JRSC on my Civic SI. For these reasons:
1. Detonated like a mofo. Detonation = BAD :jigglemad
2. Improvement in low end torque was WORSE than my turbo Civic EX. Note: EX has less torque to begin with.
3. Cost was higher. In my case the JRSC + fuel pump had a higher MSRP than the GReddy turbo kit.
4. HP gain was a friggin joke. With the JRSC, AEM CAI, 3" Thermal exhaust and DC Sports header, I was running 15's :jigglemad (This was at mile high altitude, however. At sea level I would have run mid-14's. Still, a joke. The turbo EX was running high 13's at sea level.)
5. Installation was actually harder. A well built turbo kit is much easier, with the exception of the oil return hole in the oil pan. The JRSC install took longer and puts you in weird positions to tighten some of the bolts. Plus, you must be careful rerouting the water lines. One of mine was cut by the manifold within two weeks. Very messy.
This was just my $.02, but I believe every strength of the JRSC can be countered with a quality turbo kit.
1. Low end torque - the correct turbo kit can do this. Just don't get too big of a turbo
2. I can't think of any others...
Well, good luck with your choice, just wanted to let you know what I thought having owned a JRSC Civic and a GReddy turbo Civic.
Peace.