Lax vowels, remember, are short. Tense vowels are also called long vowels; this name is slightly misleading because, in RP English at least, the tense vowels have variable length; they can be much longer than the lax vowels, but under certain conditions they become clipped, or shortened to roughly lax vowel length.
Tense vowels, then, have more variable length than lax vowels.
Tense vowels can be unchecked; that is, they can occur at the end of a word.
Here are the tense and lax vowels together in one chart: What does "TENSE" mean?