Just to try and simplify matters that have been brought up in this thread.
The new 8.33 kHz frequencies are essentially interwoven with the 25 kHz frequencies that have been used for years previously.
Unfortunately the digital frequency displays don't do the thirds rounding of frequencies that well, so the frequency on the display may be slightly off from the frequency your radio is actually tuned to.
The newer 8.33 kHz radios have narrower filters fitted in the transmit and receive circuits. This makes accurate tuning more critical if you are to be able to receive or transmit on a particular frequency.
Visually the difference is like looking at the world through a panoramic window, or through a series of smaller windows with shutters that only let you look at the view through one window at a time. The whole view is still available, its just that you have to focus on a narrower view in any particular direction than taking it all in at once.
In the case of trying to tune one of the old 25kHz frequencies, you may have to tune one channel above or below the frequency you would expect to be displayed in order to make contact. This is because your receiver has a much narrower bandwidth. You need to have the carrier frequency of the ground transmitter inside your receiver bandwidth to be able to hear the ground station.
Ground stations using 25 kHz equipment should still hear your transmissions okay because their receivers are tuned to a wider bandwidth. The issue here is that a ground station might hear you transmitting clearly, but you can't hear them because your receiver is not tuned to their carrier frequency.
Your transmissions will appear quieter and with more background noise, compared to an old 25 kHz radio. That is because your signal is not filling the entire receiving bandwidth of the ground station receiver, so you may find reduced transmitter range is a problem.
When ground stations are updated with new equipment, the quieter signal problem will disappear because now both stations will be using equipment that is closely matched in bandwidth for transmitting and receiving.
Yes, there will be some teething problems and issues and combinations of old and new equipment are used on the ground and in the air. These problems will sort themselves out as everyone moves to comply with the new standards.
Using old 25 kHz filtered equipment will cause interference to other users and you will quite probably be unaware of it. Of course you callsign will give you away, so sooner or later someone official will no doubt make you aware of the issue.
Nobody likes change and epecially the sort that requires a fair sum of money to sort out, but the new equipment does work well and will work even better once everyone has switched to the new standard.