L-arginine: Effective in the long term?

I have seen many posts here recommending the use of L-arginine. However, I am wary of using a supplement/drug in the long term without knowing its efficacy in the long term, because otherwise it's pretty much useless. There is a study
(https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3321093/) that refers to two trials on the long term impact of arginine on cardiovascular factors, both of with have negative results. What does the thal community think of this? Can anybody here vouch for l arginine supplements working in the long term?

The cited study is in vitro observations. I don't put much stock in in vitro results. There is no necessary correlation with results within a living body. We also have to remember that the needs in thalassemia are often quite different from those of the general public, although I would argue that most people would benefit from an arginine supplement.

There is a good study about dysregulated arginine metabolism in thalassemia majors at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4452408/

Conclusions
Coagulation abnormalities, haemolysis and arginine dysregulation emerged as major mechanisms associated with an elevated TRV in this cohort of thalassaemia patients. An altered arginine metabolome has been implicated in the pathophysiology PH in a number of settings (Morris and Gladwin 2011). These data provide additional support for its role in PH-risk in thalassaemia. Nearly all human cell-types contain arginase, an intracellular enzyme released into circulation upon cell damage or cell death, but the greatest source of arginine dysregulation in haemoglobinopathies such as SCD is erythrocyte-derived arginase-I released during haemolysis (Morris, et al 2005a, Morris, et al 2005b). Although the sources and specific enzyme isoforms remain to be identified in β-thalassaemia, it is intriguing that arginase activity and concentration correlated so strongly to echocardiographic and cardiac-MRI parameters of cardiopulmonary function, a paradigm never previously described. It is possible that this may exist commonly in other myocardial disorders, particularly those associated with low GAB (Erdely, et al 2010, Sourij, et al 2011, Tang, et al 2009, Wang, et al 2009) and may provide a novel area to pursue therapeutically.

This study provides further evidence that arginine dysregulation may contribute to cardiopulmonary dysfunction in β-thalassaemia. Arginase inhibition or interventions aimed at restoration of GAB may hold promise for haemolytic disorders. These data may establish novel directions for future research in the thalassaemia syndromes and beyond.