Yes, I think “Shutttr” has one ‘t’ too many. “Shuttr” would be better. They replaced an ‘e’ with a ‘t’, but they should have just removed the letter instead. Similarly-named sites “Flicker”→“Flickr” and “Forest”→“Forrst” are still readable because a letter is repeated at most twice. “Shutttr” is harder to read because English has many words with twice-repeated letters, but few or no words with thrice-repeated letters.