*** Tl;Dr: I think this thing is neat and would buy it again.***
I've just finished using my 30L for the first time and as an alternative to glass, I'm happy so far. Fortunately, I haven't experienced any of the spigot leaks some other users have. I don't feel I did anything extraordinary in attaching the spigot or any of the other removable parts, but it went through a 14 day fermentation/ dry hop and an overnight hot water PBW soak with no leaks. I've got a MoreBeer! gift certificate burning a hole in my pocket and it will go directly to replacement seals and gaskets just in case.
Before I list my likes and dislikes, I feel my purpose for using the Speidel is important to mention. I have a 6.5 gallon glass carboy and two 5 gallon glass carboys that have suited me well and I have no intentions of getting rid of them. I purchased the Speidel for safety reasons because never really felt comfortable handling a full 6.5 gallon carboy, even with a Brew Hauler. I'm always very, very careful, but I also have a 3 year old running around, so the idea of instant accidental shattered glass was always a concern.
I knew what my give and take was going in to purchasing a Speidel so my likes and dislikes are more just for informational purposes for those who are considering one and I'm sure some of these have been mentioned before.
Likes:
Capacity - The 30L gives you plenty of head space for vigorous fermentation and the huge airlock won't easily clog. My first beer in this was a AHS Stone IPA clone and I was actually surprised that with all the extra head space, the krauzen still made it to the tip of the airlock, BUT I did have a 1x3 under the spigot side of the unit so everything would settle out away from the spigot.
Design and Safety - I think the overall design is solid. I don't feel like I'm carrying around a flimsy piece of plastic with flimsy handles. The unit and the handles feel like they were made to carry around 7+ gallons without concern, yet if I did drop it, I know it's not going to shatter and slice every body part it comes in contact with. I feel this thing would survive being dropped full from 3-4 feet without splitting or cracking.
Easy to Clean - The large hole in the top makes it very easy to get your arm all the way in to clean the entire interior. The interior is also very smooth so there aren't a bunch for places for gunk to gather and require extra scrubbing. Having a kitchen sink large enough to contain the unit while washing is also handy. Each gasket and seal is also removable for cleaning.
NOTE: If you're like me, you'll want to try and separate the spigot nozzle to try and clean it. After much examination, I determined that though I may actually get it apart, the end result may not be worth the trouble and it may not seal as good once I get it back together. For now, I'm going to let it be.
Replacement Parts: The fact that there are replacement parts and seals readily available played a large role in the purchase. I wasn't going to buy it if I had to wait weeks just replace one bad gasket.
Transferring: Transferring the finished product to the keg was a piece of cake. I'm used to using my stainless racking cane and sanitary filter along with a carboy hood to transfer which is fine and I certainly won't be getting rid of them, but it was nice to attach some 1/2" i.d. silicone hose to the spigot and go. I think I remember some back and forth about what size hose fits the spigot the best and 1/2" i.d silicone was a great fit for me. I didn't have to clamp it, but I did just to be safe. Next time, I'll skip the clamp. I also like the idea of being able to add another spigot to the top to force transfer with CO2 if I want.
Dislikes:
At this point, I honestly only have one. I've never fermented in plastic before, so my dislike may not be warranted because, science. Even after a thorough cleaning, I can distinctively smell exactly what was fermented in my Speidel and I think that may be a little off-putting to those who are used to glass. Glass retains no odor, so that's what we're used to. I'm not ecstatic about the lingering odor, but I'm willing to trade that off as a cost of using plastic. I would, however, like to say that no off flavors were imparted in my beer (that I can taste) due to using plastic and I have no reservations about using this product exclusively if glass ceased to exist.