It could be a totally legit business but there's a bit too much "secrecy" for me to trust them.
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With your service, you are clearly targetting a specific type of user and I am fit, almost exactly, (what I think is) your target audience. I'm the type of person who would be interested in using your basic, no-frills service and wouldn't need any help whatsoever doing so. You wouldn't be getting any support e-mails from me with questions like "What's an SFTP client?", "How do I download my files with Microsoft Foxfire?", and such. The time you spend answering one question like that for a user is going to eat up any profits you might have made from them.
So, your target user is advanced and technical. They will look at aspects of the business that the "average user" (I hate that term) won't care or even think about: Where is your service hosted? What's your upstream connectivity like? Where are your graphs showing your history availability? What's your backup/restore procedures and timelines (I accidentally deleted a file from your server and need it restored ASAP!)? Public SSH/SFTP servers are targeted all the time for attack. What have you done to harden/lock down your public-facing servers (if it's less than I've done to my own, you seem incompetent)?
When I noticed very little information on your web site, I started looking elsewhere for it. I found out that the company is less than a year old, the registered agent is "hidden", your "physical address" is a post office, and so on.
If I'm counting on you to securely host my files, I've got to be able to trust you. I understand why you did all of the things mentioned above (I've had LLCs w/ "hidden" registered agents because I didn't want my home address showing up in the public record, I also use a PO Box, etc.) but for a company I'm potentially trusting my sensitive data with, well, that's just not gonna fly. As a technically-proficient "advanced" user, I'm going to err on the side of caution and my paranoia is gonna cause me to say "Nope!" and quickly move on.
Like I said, you may be totally legit and have only the best of intentions, but (and this is the key part) I have no way of verifying that. None whatsoever. For all I know, this is a weak attempt at social engineering people out of their data by some fly-by-night company, and your service is going to simply disappear in a month or two. Now, I'm sure that's probably not the case, but how can I know that?
Ultimately, your target customers have to be able to trust you with their data... but how can they trust you when they don't know anything about you?
I really do wish you the best of luck with your idea and hopefully you can understand a little bit better why I can't (currently) use your service.
(Side note: if you make any changes and want my opinion or thoughts on them, I'd be open to giving it. My e-mail is in my profile if you want to reach out but -- fair warning -- I'm kinda slow at responding to non-urgent e-mails so please allow me a little time to get back to you.)