Idgham is the familiar assimilation of compatible adjacent consonants; fakk al-idgham is their explicit separation. But speakers are not always free to alternate between the two forms at will.
For “al-ajlal,” the question is whether the separated form follows authoritative usage in this position. It is not enough to note that the underlying root contains two lams; the linguistic rule governing the actual word-form also matters.
This is a question of lexical or morphological deviation, not necessarily obscurity of meaning or a harsh sound combination.