I use a similar setup with SPD-R's but tried this version out on Speedplays a while back, and I've set it up for a couple local riders. If you get a decent (i.e., laminated) strap, it has enough stiffness to stay in place fine, plus you just hold the rail while you pull it up and tighten the straps anyway (I wouldn't recommend such a setup -- on Speedplays or SPD-Rs -- for road use).
I don't feel it works as well as the SPD-R, mostly because the amount you need to move your foot to dislocate from the pedal is quite small on the Speedplays. With the strap clinched down tight, it keeps a twisting release from becoming catastrophic, but if you really tilt your foot hard, you can end up with your foot half-way held by the toe strap but disengaged from the pedal, and at that point the strap tension can keep you from reengaging easily (at least while you're underway). The SPD-R has such a larger platform, plus even if you disengage at the rear in a twist you still usually keep the front engaged. It takes a whopping action to pull your foot all the way out of a strapped-in SPD-R to the point where you don't just automatically reengage again. Unless you're enamoured of Speedplays on the track, I'd think about even doing a Look or Time -- you can attach straps to just about anything with a little ingenuity.
One other issue with Speedplays is that there really isn't any release tension adjustment, akin to what the SPD-R's have in spades. Part of why SPD-R setups with straps became popular is because you can make the release tension in the pedal so high to begin with. You say you don't put a lot of torque onto your pedals, so I'm not sure why you really need to use straps to begin with. I wouldn't recommend the track Speedplays particularly, since all they do is put a sharper angle on the edge of the engagement slot at the release point -- it means that they break free much more unpredictably than with regular Speedplays, which come free with the same force but give you a tiny bit more warning. I'm not trying to recommend one brand of pedal over another, but I do think that Speedplays are a bit overrated for the track. I didn't see a single pair at the World Cup event in LA a couple months ago, and most riders have liberty to pick pedals that work for them.