You're missing an obvious trick - if your son isn't using his much at home, play that one. (That might make him a lot more interested in playing it, too.)

I wasn't able to find much about Conservatory instruments (and nothing about that specific model). That doesn't mean a lot, there are hundreds of violin makers (or used to be.)  I'd recommend going more by your own ear that somebody's Internet review on them.

Most rental instruments (for beginners) are made more to be sturdy than to have excellent tone.  From what little I found, I'd expect to sound pretty good for a student instrument, but only mediocre when you get up to the intermediate range.

If playing your son's is not an option, and you're not sure whether you want to play or not, I'd rent.  If you don't like that instrument after a couple of months, but you do want to keep going, then look at getting one.  If you do like it, then buy it or continue the rent-to-own stuff.

If you have to sign a six month lease, so that you're looking at around $150 lost if you don't get it, rather than $50, that makes the choice a little harder.  Check with the shop. A lot of times, they have better instruments available than their standard rental units, and the rent on the 290 will probably be applicable to a better one.  Quite frankly, though, I'd try to figure out a way to make using your son's while you decide if you want to continue, rather than commit to a six-month lease.

Ah, now I understand. Yeah, an adult trying to play a 1/4 is pretty tough.

The Cannon is my favorite of all the copies they sell. I don't think you'd be unhappy with one.