The reason I use Mailerlite is they offer help at all levels and they are less expensive at the entry paid level. To get any help at all with Mailchimp one has to have a paid account. I found MailChimp just as confusing even though I only did very simple things with it. I still have my free account there because I still have books pointing to MailChimp--which is a good argument to use links one can alter without having to alter the link itself in a published book.
I have a paid account with Mailerlite, and basically I've had no problems with it other than my inability to comprehend their systems. What Mailerlite deems user friendly is not what I deem user friendly.
The fact is that there are too many systems I have to interface with as an author and I can't hop from one to another with mental agility. I'm afraid this is directly related to my ageing brain and could even be related to the dementia I expect to inevitably suffer a couple of decades from now. Then again, these companies do not produce as much clarity in their user interfaces as they imagine.
Over a lifetime, we master many, many systems, but I am not the master of every website with which I have to interface to do marketing. That part isn't even due to age. For example, many authors bemoan being unable to comprehend Facebook's bizarre ad system, or Amazon's, and so on. Some of us act very superior about it as if others do not understand the principles of marketing and the necessity of advertising, but that's actually not the issue. The issue is that what the programmer thinks is logical is not what the user understands readily as logical.
Realistically, readers do not want me to send them a newsletter more often than once or twice a month. That is infrequent enough for me to have to relearn anything complex I do with the system. As someone used to comprehending my world with ease, not being able to understand something drives me crazy. And it's a huge waste of time, which also drives me crazy since like most people I have other stuff to do than stare at a website for hours in bafflement.