A reverb is supposed to be less effective because it disappears in the mix and the compression. Especially if you put it before the amp. But a reverb has something special!
Electro Harmonix Holy Grail nano
My absolute favorite reverb. Passes much level, sounds great - from unremarkable to powerful. In "Spring" mode, it sounds like a Fender ... only without the tinny noises that I can not stand. It is also not that expensive. Great great great.
Lone Wolf Harp Reverb
The construction has no noticeable problems ... I know the Belton chip and like it. Sound-wise, it is similar to the EHX. Here I see potential for DIY - if you do not mind the expense and hold the components anyway.
The reverb pedal by Boss. As so often: The level is marginal, the sound well. This works in many applications, You will hardly use all the options.
This pedal is not good before an amp There is a digital "Reverb Unit", which already brings its own compression - Even a Fender "Champ" is with it. This can cause problems. I think it's sounding significant thinner than the RV-5. Not for harp.
Fender Reverb Unit
This pedal you can build or buy as original equipment. That is not entirely uninteresting, because you could do a lot of adjusting with the sound .... but for the most people, no option. Maybe, if you want to play in a mixer, the Reverb Unit is a champ without a speaker.