Why do alien names sound so different from each other?
Because there is no single alphabet behind them: the generator runs 5 separate phonetic systems (crystalline/Vek, gaseous/Zyr, insectoid-cosmic/K'thon, aquatic/Xalis and Nuur), each with its own syllable lists. Switching species in the selector changes the sound completely, it is not the same text with a different suffix.
What does the apostrophe inside an alien name mean?
It is a sci-fi convention marking a glottal stop or click that is hard to write in English, common in names from the Zyr'Athi species (45% chance) and K'thon (up to twice per name). It does not change the suggested pronunciation of the surrounding letters, it just signals a phonetic break.
Can I keep generating the same species, to stay consistent within one universe?
Yes: instead of the "all species" theme (which rolls one of the 5 species with 20% odds each), pick a fixed species like "Xalis" or "Vek'Tar" so every generated name follows the same phonetic system, useful for naming an entire civilization without mixing sounds.
Which species has the shortest, easiest-to-pronounce names?
Vek'Tar tends to run shortest and hardest, since it leans on double-consonant syllables with almost no vowel most of the time; the most "pronounceable" for most readers tends to be Xalis, since it is the only species whose every syllable carries more vowels than consonants.