First context, I lived most of my adult life in the US, it's just right now I'm in the UK. My background is NOT LE but large scale IT.
A FST IS by definition subjective, based solely on the LEO's subjective opinion. You can argue they are trained but it is unarguably subjective. A subjective test which will be entered into evidence against you. Like I said I have zero problem with using a handheld beath test to achieve the same objective, it is based on facts not opinions.
I wasn't clear on the intimidation comment, so to clarify. An LEO can use intimidation to coerce you into taking a FST. It runs along the lines of "Consent to the FST or will have to take you to jail for an blood test or an evidence calibrated beath test as we don't have a mobile test" (mobile tests are not accurate but are good enough to generate probable cause for an arrest).
And yes there are still some PDs that are accused of having DUI arrest quotas
The Washington Post By María Luisa Paúl Ammon Fepuleai said he didn’t have a single drink on the night of Nov. 7, 2023. But when he pulled up to a Honolulu police sobriety checkpoint, an officer claimed to smell alcohol anyway. Body-camera footage later showed Fepuleai followed instructions...
www.acluhi.org
A woman claims she was pulled over and handcuffed for no reason, blaming what she claimed is a quota system to make DUI arrests. The department denied it has a DUI quota system.
abcnews.com
Is it true, I don't know but I see no reason to agree to a FST
The solution is just have a handheld unit problem solved.
As for the differences. All cops have handheld units, FST does not exist here.. Penalties for DUI are MUCH harsher of which I very much approve.