You've pretty much described my journey with 5ers - had a few - didn't gel with any of them so moved them on. Since getting my Lakland 55-01 I've enjoyed the experience a lot more - even though it meant re-learning a lot of techniques - that "Floating thumb" thing was so frustrating initially but now seems like second nature. Also fitting in notes on the low B can be like a little puzzle but I'm enjoying playing octaves "the wrong way" - e.g. finishing on an E on the third (A) string and flicking to the E at the fifth on the B.
Your point about the HB being lightweight is very interesting - I assumed that most 5ers would be heavier than the typical 4 string but at less than 9lbs I can see they will probably get quite a following.
I'm also not a fan of Tort guards - in fact I think I only have one, maybe 2 basses with guards at all. Agree that yours would look much better with a black plate, maybe Carbon fibre effect?
Had a quick look online and seen prices (none in stock at Thomman surprisingly).
And it's only £118/€132 for the MB-4 and £128/€142 for the MB-5.
https://www.musicradar.com/news/harley-benton-gets-sleek-with-its-new-mb-4-and-mb-5-sbk-deluxe-series-basses