Owner of the Gigaset A420A, I can't remember for how long (same features plus answering machine, illuminated keypad, works fine but some buttons are difficult to press due to use), owner of the Gigaset AS405 for a year and a half now (illuminated keypad) and now owner of the A690.
Apart from the design, personally I don't find any difference in practice between the AS405 and the A690 (the first one has been discontinued).
The menu of Gigaset is the easiest and most intuitive I have encountered so far (Panasonic's is exactly the opposite, always for me).
Nice large clear screen, illuminated keypad, loud ringtone (I always use the Midnight one which is not annoying), excellent call sound and volume.
Like with other Gigaset phones (and not only), ignore the batteries it comes with and use Panasonic eneloop for DECTs or any 800-1000mAh batteries you want.
Just like the AS405, the A690 also paired with the base of the A420A, which means that the bases of the AS405 and A690 are only for charging. So, 3 DECTs, no cables anywhere except for the base of the A420A where the others have been paired. Very easy process [which is why in the photo on the screen you can see "INT3", it is the 3rd DECT paired with the base].
Another good thing about Gigaset is that with very few clicks, you can copy contacts from one DECT to another. A lifesaver in my case.
The only hiccup, even with this one, was that it came with the menu in Spanish or something like that. In 2 minutes (looking at the manual, given that I don't speak that language, whatever it was) I had switched it to English and everything was OK. I saw that it also has Greek, in greeklish format, but I didn't bother.
For me, this Gigaset is also a 5-star product.
P.S. It is very easy to download Greek and English manuals, so no matter what language the phone or manual is in, I personally don't consider it a problem.
P.P.S. Of course, when you put the DECT on the base and it doesn't stay on all the time. If someone has such a problem, they probably have an issue with either the DECT or the base. If they also occasionally hear the characteristic sound when placing the DECT on the base for charging, then I can confidently say that either the DECT is not properly seated on the base or there are issues with the contacts on the DECT and/or the base. This applies to any Gigaset I have, while the only one where I have occasionally seen it is on my old A420A.