If you are thinking about buying an Osmo Mobile instead of an Osmo or the new Osmo+, you might want to consider the following points. I have used the Osmo Mobile for some days now and this is what I have noticed.
Smooth shots, the very reason you want to invest in a gimbal, are possible with the Osmo Mobile with some practice, but only the Osmo allows to attach a Z-Axis stabiliser to reduce vertical movements even more for those truly cinematic camera movements. Alas, the Z-Axis stabiliser is not compatible with the Osmo Mobile.
2. Battery life
Very long videos (e.g. timelapse) are not possible with the Osmo Mobile. This is not the Osmo Mobile's fault, as its battery lasts for up to 4.5 hours, but because of the limited battery capacity of your phone. The Osmo and the Osmo+, however, can be connected to an external power source and just soldier on. Sure, you could use your charger for your phone or an external battery pack, but the cable might get in the way and since the weight of the cable also affects the gimbal, you would need to re-calibrate your gimbal. You would also need to find a way to attach an external battery someplace, so a roll of Gaffer tape might come in handy.
3. Seeing what's going on
With the Osmo Mobile, your mobile phone is both your camera and your screen - obviously. As long as you keep the gimbal right in front of your eyes, this is no problem. But for low or high shots, you can't really see what's going on (I can't, anyway). It only gets worse when attaching the Osmo Mobile to the extension rod. Fully extended, your Osmo Mobile, along with your phone, is about a Meter away from you and the screen won't necessarily point towards you. With the Osmo, you have no problem keeping an eye on the footage as the mobile phone may be attached to the grip in front of you and not a Meter away. This becomes even more of an issue when placing the Osmo at the tip of longer extension arms, such as a microphone boompole or on a mount such as the vehicle mount which may put your camera quite some distance away from you.
With the Osmo you can always see what the Osmo is seeing, plus, and this is a big plus, you are also able to steer it even from a great distance, right from the screen of your phone. This is not possible with the Osmo Mobile. You just push the record button and hope for the best.
4. External microphone
Your mobile phone's microphone quality is okay but for better sound you may want to use an external microphone. The original Osmo has got an external microphone input, the Osmo+ even comes with an extra microphone in the box, the Osmo Mobile has got neither. You need to attach an external microphone directly to your phone. The cable may limit gimbal movements and you also need to re-calibrate your Osmo Mobile. Cumbersome.
Where I live, the Osmo Mobile is 339 Euros, the Osmo 659 Euros, the new Osmo+ 749 Euros. Is it worth it? Up to you, but I am seriously considering selling my Osmo Mobile and upgrading to an Osmo.