Friedrich in England
In this case Friedrich would remain an obscure inconsequential figure; Massive economical and military reforms were already implemented by his father ("soldier king"), so the survival of the kingdom is assured for the first.
Now I try to develop a timeline from it...
With no religious tolerance proclamation, (partial) press freedom and rule of law, the massive influx of highly skilled Huguenots from France does not take place. Prussia remains a backwater, with hardly anything distinguishing it from any other of numerous mid-sized German states.
Finally it is annexed by Austria (or Poland, or by Saxony) a few decades later after a succession crisis leaves the royal family without a heir. End of Prussia.
Now to the rest of Europe; Napoleon appears close to OTL (let's assume he is not butterflied away) and suffers imperial overstretch as OTL as well.
...I am not aware of any connection that would stop French Revolution if Prussia is gone...
However without the Prussian troops his loss at the Waterloo equivalent (probably somewhere other than this obscure place in Southern Netherlands) is far less decisive, and he is able to negotiate his way to remaining on the throne, although in a pretty much castrated France (Talleyrand is not leading the negotiations in TTL's Congress of Vienna equivalent, as Napoleon insists to take it in his own hand; with his more straightforward, aggressive ways, he achieves far less).
In Germany the Vormärz period goes similarly to OTL, except that Austria dominates the Bund unopposed; in France, however, the popular resentment is far stronger than in OTL. The revolution of 1830 (give or take a few years due to butterflies) is far more violent and results, instead of the inthronisation of Louis Philippe, in a second reign of Terror.
However, this time France is much more weakened, and also divided along the economic lines; Austrian-dominated Bund successfully intervenes in the resulting civil war, restoring order under an even more weakened Napoleon II, who is rescued from death literally in the last minute by an Austrian unit. Austria uses the intervention as a catalyst to unite Germany in a similar way Prussia did OTL in 1870-71. On the other hand, Austria suffers from a few problems OTL Prussia doesn't have; Hungarian nobility wants to have more say in the Empire (hard to butterfly this away, it is pretty much built in in the A-H structure) and also other parts of the empire want to use the moment of distraction; either to break away, or to get a better recognition in Vienna.
(Would Russia try to use the opportunity and to grab something while Austria is distracted? Or would it support Austria as in OTL, afraid that secessionist movements will spread? What do you think?)
Any comments? Suggestions?