The Schertler BlueStick is a great under saddle pickup for a reasonable price, but the odd batteries have always seemed a deterent to me. There is something to be said for being able to pick up a 9 volt at the corner gas station if you forgot to pack spares to a gig.
As far as the Schertler DYN-G, I've heard it on flat tops and mandolins, and it does sound very good. Even though top transducers are inevitably more prone to feedback than USTs, this one seems a little better than most. Still, it's not as feedback resistant as a UST, and many players find anything attatched to the outside of thier guitar to be a bit of a nuisance. I may recommend it for mandolin, but not generally for guitar. The price is certainly a factor. For many players it seems that being able to plug in and play without having to concern themselves with placement and whatnot seems to be a appealing quality. Often even enough to outweigh slight differences in tone quality, especially if it can be reasonably compensated for with a good preamp.
I certainly agree with Jim about thier amps though. They are hands down the best acoustic amplifiers I have ever plugged in to. Unfortunately I have to say that if you want it to sound like it's natural self through a few high quality condenser mics you will have to go in to a sound room and play it through a couple high quality condenser mics.  Perhaps someday a Baggs, K&K, Schertler or Fishman will give us the golden egg, but I'm not holding my breath.
I tell all my customers that they have to choose a different level of comprimise between convenience, tone, feedback resistance, price, etc. For an acoustic playing with a drummer, electric guitar, bass and vocals, etc., the UST is usually the best choice. Not quite as natural, but still very good, convenient and feedback resistant. For an acoustic duo setting a top transducer may be more appropriate, or a combo like the Baggs Imix. There are still some good magnetic pickups out there, especially appealing to the non-commital type who need everything completely reversible. For a solo concert classical player, sit down and put a good mic on a stand. I've never really been a fan of external top transducers. There is no "best" pickup in my experience, only the most appropriate.
I know you just wanted opinion, on the Schertler and probably have your own opinions on pickups in general, but I'm always just too happy to share my thoughts. 
P.S. - Tone/convenience/price ratio, I think the K&K was a wise choice over the Schertler.
David Collins39016.468900463
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Street price is around $375. Retail on the BlueStick standard version is $225, $325 for the active EQ version. The BlueStick is a cool little UST ... not piezo. It's actually a tiny mic inserted into a tiny rectangular tube!
I can only imagine what one of those would be worth if the DYN is $450 !!!