Yes, the faster velomobile models (Milan SL, Bülk, Snoek, DF, Alpha 7, Milan GT, Quest, etc) are really that fast! The "slow" models (Quatrevelo, Strada, Mango, Hilgo, Alleweder) are still pretty quick, though.
While its true that velomobiles are rather slow at real climbing due to their weight (24-26kg with hood), in a "rolling hill" area like Northern Germany, they get so much speed and momentum on the slight downhills, that they almost coast over the next hill. I've once bombed down a short 13% slope, reached 90.8km/h at the bottom and "flew up" the next 12% or 13% hill, while still maintaining 55km/h over the top. Its flabbergasting and a totally different riding experience than you have with any other cycle. At night, going down gentle slopes at 80+ in my Milan GT, it feels like pedalling a human powered fighter jet.
Depending at the velomobile model, wind gusts or truck vortices are an issue though. Some models get easily blown all over the place (Quest) while others (Milan, Bülk) are relatively unfazed. Strong wind from the front or rear is a non issue, you hardly feel anything. Strong sidewinds propel especially the Milan and Bülk quite noticeably. Its amazing to "coast" with minimal effort at 70-75km/h in a 30-40km/h side wind.
Velomobiles are most at home on open country roads with gentle slopes. They kind of suck in stop-and-go city traffic, though. Also, not only strong riders benefit from the huge aerodynamic advantage, but riders with "normal" power output will greatly benefit as well. I'm one of the latter.
Here is very good explanation why velomobiles are so fast:
Take a look at the numbers of this guy in his Milan SL at a -1% slope:
An other Milan SL rider in a short all-out sprint: (the guy is a masher, who skipped a few gears sprinting)
A very good source is Saukki from Finnland, he got loads of contents regarding velomobiles in his Youtube channel:
Most questions about velomobiles are answered in the
Velomobile Knowledge Base:
https://anotherkiwi.gitlab.io/velomobil ... ledge.html
The go-to online resource about velomobiles is the (english friendly) German Velomobile Forum. Most velomobile designer, manufacturer, dealer and top racer (IIRC all current 6h, 12h and 24h world record holders) are members and post more or less frequently:
https://www.velomobilforum.de
The German Forum is also one of the biggest markets for used velomobiles:
https://www.velomobilforum.de/forum/ind ... omobile.12
If you look for a new velomobile (I'd strongly suggest you do some test rides before!), go here:
https://www.velomobileworld.com
Since John Williams closed shop, I think the only velomobile dealer on your side of the channel is Laid Back Bikes in Edinbourgh:
https://laid-back-bikes.scot
Update:
According to the Velomobile World Ambassador program, you have at least two 'velomobile ambassadors' in England:
https://www.velomobileworld.com/ambassadors
Nick Tulloh in Oxford:
https://www.velomobileworld.com/ambassa ... las-tulloh
and
Joel Bradley in St. Neots, Cambridgeshire:
https://www.velomobileworld.com/ambassa ... el-bradley