I have a Lak 17A with FES. I had the glider already, so a retrofit
sustainer was the only option. I chose the FES for those features which are
undoubted advantages compared with an internal combustion engine/pylon. My
reasons and the outcome are set out in two articles which are available on
Luka’s website.

For somebody contemplating a new glider, or for a manufacturer
contemplating choices between one route and another, I think there are a
number of unknowns. These include the reliability in starting in the air,
general reliability, relative safety, hazard warning, longevity, ongoing
maintenance costs, battery replacement costs, etc..

My personal opinion, based on very limited numbers of FES and jet, but
rather larger numbers of internal combustion engines, is that:

FES reliability is unproven, but I have no reason to think that it will be
anything other than good. I have a friend with a Lak with a sustainer
engine who has landed out several times after it failed to start in the
air, with of course a considerably higher decision than the FES needs. The
jet is claimed to have a low decision height and quick start up, but I have
heard of one user who is onto his third engine which does not sound like
good reliability to me, if true. I have no idea whether the jet is close to
100% reliable starting in the air.

Lipo batteries based on model aircraft flying and some other applications
have a reputation for occasional disastrous fires. The FES system has
temperature sensors and warnings which give me some comfort. I have a
photograph of fire damage caused to a glider with an internal combustion
engine. The pilot did not know until he was landing or had landed that it
was destroying the fuselage behind the wing. He was very lucky he was not
cruising high at the time. I suspect that the jet has too little service as
yet for anyone to know whether it is better or worse.

FES Battery replacement costs are likely to be 200-500 units of currency a
year on average, maybe less. Electric motors are usually very reliable. I
don’t know about the control system. My friend with the internal
combustion engine is having cracking problems with his exhaust system.
Others have too. I don’t know what other routine or sporadic maintenance
costs are involved. I don’t suppose anyone can say what they will be for
the jet, although for someone to be on his third motor is not an
encouraging sign.

I’m certainly very happy with my decision. The range is okay, as an early
adopter I don’t have some of the features now available, but it was the
right decision for me at the time. For other people, and in the future,
there may be good reasons for different choices. In my opinion, nobody can
yet know.

Chris N