I can't believe people are still using older heater technology like Eheim Jager. As far as glass heaters go, they are probably the best, but here's some things to consider:
-They can and do still fail, like almost any heater not run on a controller
-They can shatter during water changes, even if you have a heater guard
-The additional expense of a heater guard if you want one
-They are pretty big... the 100 watt heater is like 12"!
-You have to reach your hand in the tank to adjust the temperature
WHY would you not use a titanium heater? They are bulletproof (don't ever shatter, don't need guards), come with external controllers that you can adjust outside the tank (and prevent them from failing), and they don't even cost more.
I would recommend the newer finnex titanium heaters... they were having issues with the controllers on some models... this is the new one that is supposed to be better... I haven't used it:
http://www.aquacave.com/searchresult.aspx?CategoryID=636
I have used the aquaheat but the controller gave out on me after 6 months... didn't cook my fish or anything, it just clicked on and off and I noticed it right away from the noise. But your best bet would be to throw down $100 for a really quality controller like a RANCO... then you can use any heater you want.