When comparing LessPass vs Buttercup, the Slant community recommends Buttercup for most people. In the question“What is the best cross-platform password manager?” Buttercup is ranked 10th while LessPass is ranked 11th.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Open source
Pro Really platform-free
Works everywhere, in any device that can run javascript.
Pro Doesn't store passwords
If it's not stored, it can't be stolen.
Pro Can be installed with home brew
Pro Open source
There's a large base of developers who work on improving the software.
Pro Import other formats
Import passwords from other password managers including 1Password (.1pif), KeePass(.kdbx), and LastPass (.csv).
Pro Good UI
Pro It's free
As in beer.
Cons
Con Deterministic
Deterministic password managers have many drawbacks.
Con Cannot store existing secrets
Existing secrets (aka passwords) cannot be stored with deterministic password managers. In order to use LessPass effectively, you will need to change your password on every site.
Con Easily cracked with exposed/compromised master password
Since anyone can use LessPass with the same parameters as you, all they need is your master password (which could be obtained through keylogging or numerous other methods) to gain access to every one of your site passwords.