My experience is with Melanotan 1. It's supposed to be much safer than 2, and the only time i need a huge libido is on vacation where i can't bring it anyways.
From what i hear Melanotan 1 works about half as well for tanning, but people can also use huge doses with very little side effects other than about 2 hours of upset stomach. The upset stomach on 150mcg is non existent.
I use it for sun exposure before going to the tropics, etc. 150-500mcg. I'll go from really pink and sunburned, to bronze by the time I wake up. It really saves a vacation when you're ultra white and want to be hanging out at noon on the beach. Use with sun, or tanning for 2 weeks beforehand IMO.
For research on Melanotan 1, look up Afamelanotide, which is used as a time release 16mg skin implant. It dumps multiple MGs in the first day, and makes me feel very safe about using more than 500mcg if I wanted to feel like shit for the day.