I haven't had leaks in my brewbuckets beyond the o-rings wearing out, but they were years old at that point, and even then emergency bubblegum for that brew was a matter of giving the spigot a tiny twist. I've had my buckets for 5+ years and I'm still on the spare o-rings that came with the buckets.
I take the spigot off for every cleaning. To assemble, I screw the nut on snug, grab hold of it with my fingers, and give the spigot a ~60-90 degree turn with my other hand. Since I don't use the "rotating" racking arm -- it should be called a joking arm -- the spigot is in a static orientation until disassembly, and I can tighten it slightly more than if I was planning to turn the arm.
I think I've stacked mine once. It does work, but the setup doesn't induce confidence if there's actual liquid in the buckets. Plus, if you want to lift the top one off or touch it in any way, know that the lids flex worth in the order of 1dL: you'll get suckback with an airlock if the pressure applied on the bottom lid diminishes. The ones in the photo are almost certainly empty (many lids are not latched), and I wouldn't dream of stacking them 3-high when full.
I also think they are overpriced for the build quality, and I got them cheaper than the current MAP. I was at one point considering getting 33% cheaper and 20% larger replacements, but when I saw welding seams on the inside I reconsidered. The brewbucket is one smooth surface, so at least that's done right. I also find the spigot useful, also for gravity-driven closed transfers, and would not get a fermentor without one. Some of the fancy fermentors with 57 triclamp ports look nice, but I cringe when I think about cleaning; I guess it works if you have a CIP setup. The choice to put the thermowell on the lid in the "improved"[-in-price] brewbucket 2.0 is a dealbreaker for me, so if the originals run out and I need another fermentor, I'm not getting a brewbucket.
So, I can't really recommend brewbuckets, but I can't currently recommend anything else either, and if you want stackability, it works, at least sort of. (oh, and I paid for mine with my own money, as you can probably deduce from actual criticism towards the product)