Letrozole is an AI and its effects are only the result of lowering E2 levels.
With more input on a situation, I often suggest 0.5mg anastrozole per week in EOD divided doses.
Letrozole dose/response is not very predictable and results can be harsh.
The result depends on ones age and HPTA responsiveness. For guys with low T and low E2, lowering E2 will only add to the misery they feel.
When you read the old studies where young normal males were given an AI and T increased, the results do not apply to every other situation.
If it works for you; great!
Obviously the benefits to those with primary hypogonadism are low.