Arabic has so complex notations that a word is written differently when it is at the beginning or in the middle or at the end of the sentence -if I'm not mistaken of course.
No, that's wrong. The words aren't modified by their position in the sentence, but the letters in the words are. I don't think the change to the latin alphabet was done due to convenience (or at least this wasn't the main reason), it was more of a stage in the westernization process.
After all, arabic has served many different languages and most large groups of its users have modified it a bit to suit their needs. Ottoman turkish did that as well, AFAIK.
In the end, it's all about how accustomed one is to each system. I 'm sure children who learn arabic won't be needing much more time to memorize the 3 forms of each letter (some of them have only one tho, I think they 're 6 out of 28), and no small case letters as well. I remember that a couple of years ago I had learned most of the letters over the course of something less than a week, using a system similar to this one, I 've heard it's quite popular lately (shows only the basic forms):


And japanese kids do learn 2 different alphabets of 48 letters each (similar to a significant degree tho), apart from the kanji/ideograms.

Maybe Turkey lost some of that "exotic" feeling along with the abolition of the arabic alphabet. OTOH that made the language much easier for westerners to learn, getting down straight to grammar, syntax and vocabulary.