Welcome to the forum!
The Tera Echo and the RE-20 are actually two very different beasts.
The RE-20 is a very good emulation of the old tape echo box . Those old delay units work with tape bands pretty much like a cassette player. The sound is recorded by a tape head and then played back by a few read heads, thus producing an echo. The overall sound cannot be compared to crystal clear digital processed delays. It has a flavour of its own. Analogue BBD delays like the old BOSS DM-2 (or the new DM-2w) do again have an own sound, but that's another story. I don't really want to confuse even more.
On the other side the Tera Echo is a fully digital unit that doesn't intend to sound like an analogue unit. BOSS produced this one to make a totally new sound available. I have never played one so I cannot tell you the difference from first hand experience. But it does not generate the same sound as the RE-20. Not a bit.
We're talking about apples and oranges and you have to taste it to know the difference. I think it's the best to watch a few good demos of both units at YouTube so you can hear what each one sounds like.
Small question: what do you want to achieve? What do you expect from a delay unit for your playing style?