So, I guess that means you can read it when it's horizontal.
Truth is, it is pretty obvious. It is no different from reading English vertically of which, is not natural but not impossible to understand. The Manchurian Font and KeyMap are the start of the New Manchu Era, the final goal is to be able to use the Manchu Script on the Internet written in the style which it is intented. For now, we have to settle it written horizontally.
Also, about the sentence 【ᡝᡵᡝ ᠣᠴᡳ ᠮᠠᠨᠵᡠᡳ ᡥᡝᡵᡤᡝᠨ ᡳᠨᡠ】ere oci manjui hergen inu
, this is what we would write but, in speech it is allowed to shorten the phrase to: 【ᡝᡵᡝ ᠮᠠᠨᠵᡠ ᡥᡝᡵᡤᡝᠨ】ere manju hergen
or 【ᡝᡵᡝ ᠮᠠᠨᠵᡠᡳ ᡥᡝᡵᡤᡝᠨ】ere manjui hergen
. The difference between 【ᠮᠠᠨᠵᡠᡳ】manjui
is akin to the difference between "Manchurian" and "Manchu".
I am curious that, where did you learn of the Daicing Manchu Font and KeyMap? After all, it is not really that popular, more so outside the Manchurian online communities.