Like a lot of mass produced herbal extracts, the companies making them are relying on scientific data rather than traditional data.
In the spring you harvest the hawthorn flowers, leaves and twigs. You tincture those, fresh (not dried). Then in the fall you harvest the berries and add them to the spring tincture. You need all parts of the plant for it to have the cardiovascular effect. The big companies making extracts don't know this because they don't consult traditional herbalists. Instead, they read studies and then do what they think is a proper extract. You can use the berry extract but it won't be nearly as strong as using the whole plant; but you need to harvest different parts in different seasons, which the drug companies aren't doing because it's too time consuming or they don't know, which is why their products tend to be inferior.
The same thing happened with echinacea. Studies claimed it didn't work yet they weren't using the right part of the plant or using the plant at the right point in the illness, so of course it didn't work; and most extracts on the market are haphazardly produced from any part of the plant, or from inferior plant material.
If you use hawthorn extract that is made properly, it will lower blood pressure within 24 hours and keep it there as long as you keep taking it. But it's not meant to be used as a blood pressure medicine. It's actually a cardiovascular tonic. It slows the heart rate over time by increasing the thoroughness and strength of each contraction (volume efficiency), and this in turn lowers vessel tension.
I don't know the mechanism by which it lowers cholesterol, I just know that it does. The Chinese have been using it for this purpose for over 2,000 years, before they ever knew it was cholesterol they were treating.
IMO if you want to lower blood pressure using herbs you should consult an actual herbalist. Your blood pressure could be for any number of reasons. Hawthorn is not for "high blood pressure", it's for poor heart muscle tone. Some people have high BP due to liver issues, like poor portal vein circulation, or their liver is filled with junk that needs filtration; or maybe the person's life is so stressful that they're always riding on cortisol; or maybe their diet is horrendous. Herbs are not meant to treat symptoms, you have to look at the whole medicine. Modern medicine / western medicine treats symptoms, which is why when they dabble in herbalism their products tend to fail. It's because herbal formulas take the whole person into account, rather than a symptom. You can't make a one-size-fits-all formula for everyone who has the same symptom. Ten people with the same symptom could have a different root cause.