In summary, the two are different!
- “taso, …” is particle-y and “taso la, …” is using taso as a content word like how it works as a modifier.
- “kin la, …” uses kin as a content word like how it works as a modifier
- “kin, …” is pretty rare but it usually is used to mean the same thing as “kin la, …”
taso at the start of a sentence is different from taso as a modifier. Here’s taso at the start of a sentence: taso between two different sentences, at the start of the second but without la says “these two sentences are related; the second is clarifying or contradictory to the former.” It’s like “But, …” or “However, …” in English!
For comparison, “taso la, …” says “the idea expressed by this sentence is exclusive in some way”, for example “taso la mi pali e ilo”. I exclusively create tools. This is using taso as a content word, and makes the entire sentence “exclusive” or “only.”
This sentence-start taso is sometimes analyzed as an interjection, but that would imply it could be used elsewhere with this meaning; I consider it to be part of the sentence.
kin is usually a modifier, like taso. It has no common-use reason for being at the start of a sentence in the way taso can be (i.e. without la), but you often can do “kin la, …” which is to say “the idea expressed by this sentence is additional to something else,” kinda like leading a sentence with “Also, …” in English. Some speakers use “kin, …” without la to mean the same thing, but it’s pretty rare.
The inconsistency in function is a matter of usage, in my experience; people understand “taso la, …” differently from “taso, …” because of [taso] content word in the former, and taso’s unique sentence-start behavior in the latter.. Whereas in kin, “kin la, …” is likely the same as using “kin” somewhere in the sentence as a modifier.