The spelling of Manx, unlike those of Irish and Scottish Gaelic, does not represent the Goidelic phonology, and more closely resembles an English-speaker's attempt to write Gaelic. This is because Manx developed without a written literature, and when attempts were made to introduce a standardised orthography for the language, the choice was made to spell the words in an English manner. For example, 'Isle of Man' in Irish or Scottish Gaelic would be written as Oileann Mhannain, whereas in Manx it would be written as Ellan Vannin.
This had the unfortunate result of making the spelling much harder than that of the other Gaelic languages, as many Goidelic grammatical features were lost in the process.