Although I honestly and readily admit that I am not proficient in Volapük, I think it has had something of a bad press over the years. I do not consider it entirely a priori, as I can recognize some roots in it with little difficulty. Also, it is highly logically constructed and extremely regular, perhaps even more so(!!!) than Esperanto (in which words ending in -aŭ can fall in three different parts of speech, for instance). How many monoglot speakers of Mongolian (to pick a random example) will recognize many (if any) of the Indo-European roots in Esperanto? Many (not all, of course) users / learners of E-o are IE speakers, to whom it is "easy." To monoglot speakers of non-IE, highly inflected languages, it is conceivable to me that they might even find Volapük to be easier than E-o.

Volapük likes to use as few words as possible - where Esperanto uses prepositions or separate words, Volapük is happy to slap on an extra affix or three - e.g. gudiko=bone, gudikumo=pli bone, gudiküno=plej bone. In some cases, this permits it to be exceedingly brief but precise - öbinob is, I was going to have been here.

This has a certain aesthetic attraction, for me anyway, but long-term it is liable to cause more confusion.

I love Volapük, too, since I've learnt it 20 years ago at the same time as Esperanto. pulöfoföl "(a woman) who will have been loved" - wonderful. On the other hand Volapük doesn't make use of internationalisms as much as it could (still keeping the syllable structure simple), the grammar is bloated (even more the affixal system), and especially Volapük I is full of German biases.
I use it from time to time to note numbers other people shouldn't see. Esperanto, however, doesn't really work as a secret language, too many easily recognizable words.

Looks like Volapuk is certainly an interesting thing and perfectly suits to be a 'secret language', while Esperanto is quite transparent for native Romance languages speakers (in most cases). Thus, Volapuk's cryptographic value is doubtlessly higher.

I use it from time to time to note numbers other people shouldn't see

I just make the reasonable assumption that all burglars, or other invaders of my privacy, will not be Esperantists or linguists.

What about Esperanto with Ŝava Alfabeto?

Reasonable. A number of years ago I had a rather eccentric hobby interest in old (English language) shorthand systems. One of the points brought up by authors a few centuries ago was that if one wrote in one of these old shorthand systems, one's notes, diaries, journals, whatever, would be less likely to be readable to prying eyes. Writing Esperanto in the Ŝava Alfabeto would be even more private, although theoretically there might be some E-ists who would see your diary and happen to know the alphabet. But unlikely.

That is interesting; I suppose one could learn to read it as quickly as their usual alphabet, given enough time. I have a friend who can write in some other alphabet... what did she call it?... "dragon writing" or something. I think she said it was something from a fiction series or something. Sorry, my memory on the topic is a little fuzzy . Her brother knows it too, so they can use it for secret messages.

I have a few things like that; when I was a kid I made up an alphabet code I called Cadianese (cad for crosses and dashes and ianese to sound cool). But I didn't do much with it, so I can't read or write it without the key, and I also never adapted it for Esperanto. After that came the qwerty-flip code (ey swwdl sedi ygel), but that also is too much effort to read and write, and it lacks apostrophes and quotation marks. Sometimes I write Esperanto with Cyrillic letters, which isn't quite top-level security, but it's enough for any purpose I'd have, and read/write-able enough for me.

The easiest for me, but also the least effective for encryption purposes, is to just write backwards. If I write backwards in Esperanto, it's pretty safe from those who didn't care enough about what I wrote to go through any effort to decipher it, the casual diary-reader types. And at the same time it doesn't at all hinder my own reading and writing. But usually I just write Esperanto in the standard direction, that's how my journal is written, and apparently that was enough encryption to deter my brothers. And it's the only thing that does!

johmue:

I also regularly use Esperanto to pretend that I don't speak neither the local language nor English. For example when mormons or someone like that approach me.

Haha brilliant, sounds like me every time a phone seller calls.