I've been using CE3s since they came out with no real burnt taste other than when the run out of liquid. I mix my own liquids at 60/40 and have no problems with wicking. I do "wash" them out before first use to get ant primer or machine oil out. I can tell you the primer tastes like old socks!
I would suggest washing them after every third fill or so. All you need to do is pump clean, hot, water through using the filling syringe. Of course, do this over a sink because it does get a little messy. Simply fill the syringe with hot water and fill the CE3 the same way as you would with liquid. Once some water is in it, and it may not actually fill all the way because water molecules are small enough to get through the wicks easily, pump the plunger up and down to force the water left in the syringe through the CE3. I usually do this using a 5 or 10ml syringe to get lots of water through them. They can be refilled and used immediately, but the first few drags, maybe up to ten drags, will not produce any vapor as the water is boiled off.
Alternately, the mouthpiece can be removed, then the inner seal is removed. I use a paper clip with a little right angel bend at the end for this. At this point the air tube can also be removed using a pair of tweezers. This will expose the coil and wicks and allow a direct stream of water to get to them for a better cleaning. For the really adventurous, the outer barrel can also be removed to provide complete access to the coil and wicks by screwing the CE3 onto a battery and gently rocking the barrel back and forth while pulling firmly.
Thick liquids, those with over 50% VG may be slower to wick, but even then they should work fine together.
The Nano is actually a micro carto tank. That is a cartomizer inside a small tank. It does have wicking issues, at least according to some reports I've seen on them, with liquids over 50% VG. It is also much more difficult to clean. In terms of durability, being able to take some physical abuse, it isn't as strong, physically, as a CE3.
Any device, carto, clearo, CE3, Nano, T3, will develop a burned taste over time, especially if liquids containing higher amounts of sugars are used. The sugar, and other components of the liquids for that matter, do burn, carbonize, and attach to the coils. After a while the accumulation can be high enough to effect taste and performance.
Just my opinion, worth what you're paying for it. Your results and mileage may vary. No warranty or guarantee is expressed or implied. Proceed at your own risk.