That SX looks really sweet. Seems like it has a lot going for it. A good price and good reviews from experienced players. They say good things about Rondos too.
Some things you may want to consider:
It doesn't have a maple cap, just solid mahogany, so it may sound a little darker than a Les Paul, more like an SG perhaps. Did you go through Rondos other listings? They're offering a model with an ash cap for $10 more. Looks nice.
http://www.rondomusic.net/gg1stdashna.html
For $149 I strongly doubt that the pickups will be that great, although the folks on H-C think they're ok. But it looks like you could have an instrument deserving of an upgrade. You won't go far wrong with a set of Duncans, a JB and a Jazz perhaps, although you'll spend as much on these as you would on the guitar. I have a set on my Antoria (70s lawsuit) Les Paul.... actually they're the "Duncan designed" HB 102 set, based on JB & Jazz, as good as, at a fraction of the cost and perfect for what I'm playing ... classic rock ... Thin Lizzy, Bad Company etc ... keep watching ebay!
You didn't say what pickups you have in your Strat. Maybe you could swap them with the SX. If you do swap them out, throw some Lace sensor duallys in the Strat. With some clever switching you could turn this into a very versatile guitar, and it never hurts to have a backup. I'm working on something similar and hope to have it done in the next few days.
I think you may be on to a winner here, just bear in mind that $149 probably won't be your final cost. The good thing is you don't have to spend all the money at once. If your finances allow, get the hard case too.
I hope it works out for you. Go for it!
Pete