If you want L-arginine buy the powder and take it orally. It’s very cheap and likely more effective than a topical gel. Beyond that these gels tend to have something in them that irritates the penis skin (like a form of capsicum) and may cause more blood flow as the body attempts to fight off the irritation.
If you want to increase blood flow and you are 40+ maybe consider micro dosing viagra or yohimbe. Yohimbe can cause heart palpitations in the doses you would find so buy a pill cutter.
If you need either of these options you should first be looking at other things. Check your diet. Eat more fatty red meat, eat liver, eat less vegetables. If you aren’t overweight eat fruit. Get decent amounts of sleep. Reduce the stress in your life. Give up porn. All these things will increase your erection quality massively.