LEXE  I thought this program looked very promising and I really wanted to like it. Unfortunately I couldn't get it to work on my Mac to backup on a server over the internet. Despite multiple attempts of contacting the support team via support forum and emails I wasn't able to get a single helpful response within the last 6 weeks (!). So I paid good money for this program, haven't managed to back up a single file yet and am getting more and more annoyed with them. I tried to get my money refunded - also unsuccessfully.

Bottom line: Unfortunately this is not a program on which you can rely on for backups and the service and support they offer is absolutely appalling. Nice idea but nothing for serious use!  
(Version 1.2.1)

FRENZY  In theory, this is a great app. In reality, not so much. With each new upgrade something breaks (all updates made me forced to delete all backups and start over from scratch). Developers does not listen to feedback and keeps deleting threads about issues, stating "theres no issues what so ever" and "no users are having problems". Clearly they do not want any relations with the people buying their software. Theres no real added features in new versions and the software works almost exactly the way it did when THEY bought it.

Its all really a shame, because this could have been SO good, its a backup app that does its job great in the background, until it breaks/hangs and youre left out in the cold. For 49€, the very least you could expect is a friendly developer.  
(Version 1.2.1)

BORLOX  I use Twin to back up about 40 GB of data to Amazon Web Services.

Pros:

Data persistence. Amazon won't go out of business suddenly, taking your data with it. You don't need Twin to retrieve the data. If the developer disappears or the app stops working, you can still get to your backups with third-party tools.

Data privacy. Data is encrypted with the standard AES algorithm before being transmitted. You can decrypt the archives with open-source tools.

Stability. No crashes in several months of using this app.

Flexible scheduling. You can set Twin to back up periodically and/or when the network becomes available -- useful for portables that aren't always connected.

Cons:

Inefficient use of bandwidth. Data is packaged in archives of fixed size, which is decided at setup and can't afterwards be changed. The default is 1 MB. So if you change a single byte in a small file, at least that amount of data has to be sent. If you change a single byte in a large file, the whole file has to be sent. It would be better if Twin used something like librsync to back up only the parts of files that have changed.

Mirror backups only. The backup contains the most recent version of each file you've selected. There's no option for incremental backup.

No obvious warning of failure. The interface is normally hidden. The only indication of a failed or incomplete backup is in the interface. If you don't look for it, you won't see it.

Suggestion:

Offsite backup is a last resort in case of total destruction of your primary site, including your local backups. Put all the data you need to recover your backups on a small USB flash drive (encrypted, of course) and keep it with you at all times. That would include, at a minimum, your AWS public and secret access codes, your backup encryption keys, and your Twin registration data.  
(Version 1.1.2)

STEPHEN495  Fine backup solution. Works unobtrusively and with low CPU usage.

Easy to configure for both local and remote backups. I like the exclusion system in particular; its files excluded preview is very fast, along with the rest of the program.  
(Version 1.1)

ANONYMOUS  Version 1.0.1 only solve the issue with the Restore function. Version 1.1 planned for end of June will add many improvements (all updates/upgrades are always free)  
(Version 1.0.1)

GABBLE  Looks promising, but:

1) Twin is not able to use custom ports (e.g. sftp on port 54000, etc.). According to developers, version 1.0.1 was supposed to add this feature... I still see no indication in the release notes.

2) No support for incremental backups, by design. This makes some sense with remote backups, but not with mass media backup (where Twin is rather a complement to Time Machine)

3) no bit-wise comparison of files, which is vital for large files backups (images, video, vmware images,...). Every time the new file gets deleted then replaced. This is a real time, bandwidth (and money?) waste with remote backups. Dropbox and Qrecall both deal with bit-wise comparison. Unfortunately Twin developers don't seem interested in such feature.

A real pity... :-(  
(Version 1.0.1)

ROB.H  Agree, it looks promising but the would have preferred at least a time-limited fully functional 'demo'. Also, I couldn't get the restore function to work at all, not even for the single file the demo allows.  
(Version 1.0)

SPECTRAL7  looks cool to me.....will test for a bit and report back  
(Version 1.0b2)