I don't really know how to answer you. My first reaction is to say that transitive verbs (verbs that can normally take objects) never function adjectivally, but then there is the canon
lo'laH and
lo'laHbe'. I
think that Okrand used the word
useless on one of the tapes, and the phrase was
yIHmey lo'laHbe'bogh 'useless tribbles', but I can't remember exactly. If he did, then
lo'laHbe' isn't an adjective, but still a verb phrase. But maybe
lo'laH and
lo'laHbe' are special cases, or actually separate words that only resemble
lo'.
I don't understand
-laH to mean '-ful'; it means 'able to'. So I read
tlho'laH as 'he can thank (someone)', and
tlho'laHbe' as 'he can't thank (someone)'.
As for how
-Ha' and
-be' compare, in general, I would say
-Ha' creates the polar opposite of the quality word it is suffixed to, and is semi-lexical, that is, probably only attaches to certain words, and we as non-native speakers

tend to mis-use it. On the other hand
-be' just negates the verb (quality or action), and can be freely used any time. However, there are examples that contradict both ideas. It just isn't that well spelled out for us, and we have too small a sample to make hard and fast rules.
Off the topic a bit, one of the things I've seen over the years is people coming to these forums or the KLI mailing list having just discovered Klingon and very excited about it, but then they get sidetracked trying to come up with Klingon equivalents for English expressions, some of which are very nuanced and idiomatic and which don't really come up in the normal use of Klingon anyway. Then they get frustrated or bored, and eventually drift away. If you are serious about Klingon, start sending us some messages in it! If you want my critique, just ask for it (I make it a policy never to critique anyone's Klingon unless they ask me to).
mIwvam Dalo'chugh, chaq nom tlhIngan Hol laHlIj DaDubchoH 'ej tlhIngan Hol DatIvchoHchu'!