After reading a user review for the iO Series 9 here on skroutz, I decided to go for the iO Series 5 with less money (purchased for €75) as it offers a great quality/price opportunity.
- Very powerful, no comparison to the €20 Oral-B electric toothbrushes.
- Supports the Oral-B app for monitoring brushing in the 6 coverage zones (just like the iO 6, iO 7, iO 8, iO 9, iO 10 models).
- 5 basic brushing options that personally "cover" me:
- Daily Clean,
- Intense Clean,
- Sensitive,
- Super-Sensitive, ⬅
- Whitening
(I also believe that the Super Sensitive and Gum Care functions are tricks by the company to make the product more appealing - as mentioned in the review I read).
For comparison, let me mention the functions of the iO Series 6 (+€20 difference):
- Daily Clean,
- Intense Clean,
- Sensitive,
- Gum Care, ⬅
- Whitening
And I want to point out the only difference I noticed in their features.
So, I feel very satisfied with the choice I made!
A real budget option!
I highly recommend it without hesitation.
Charging took me about 12-13 hours.
(I will update on battery life)

Years user Oral B Pro 3 3500, before Oral B Pro 750 and before a Soocas X3U and an older generation Sonicare. All oral B generally clean teeth very well. After a certain point, you simply pay for design and extra functions, most of which are useless, such as connectivity with mobile phones, etc. I lost the base of the pro 3 3500 and found it as an excuse to get something new.

The brushing experience is different with the iO compared to conventional Oral B brushes, as you don't feel the brush making rotational movements but vibrating like a mobile phone, something like a combination of oral b and sonicare.

I think it cleans just as well as conventional oral B brushes, if not better, with the following differences:

+
1) By connecting to the app, you can achieve better coverage of all teeth compared to the feeling you had on your own. This increased my brushing time from 2 minutes to about 2.45 in order to have full coverage.
2) Much quieter - no longer sounds like a tractor.
3) Through the app, you have an accurate battery status, so you don't run out in the middle of brushing like with the Pro 3500 I had.

-
1) More expensive replacement parts.
2) The battery seems to last even less than the Pro 3500, but the longer brushing time and Bluetooth connectivity definitely play a role.
3) The app is not the best - sometimes it needs to be closed and reopened to connect to the toothbrush.

In conclusion, I think it balances functions and cost very well and is one of the cheaper io models with Bluetooth (purchased for about 90 euros).