1.44" diameter makes 1.6 sq in, which is 67% of the usable surface area of a Perdix, or 55% of the OSTCplus, or 35% of the OSTC4. It should be obvious that a display somehow has to compensate for the fact that it is small. The fonts in the center are smaller, less data is shown, and/or the data is more densely displayed with less space inbetween.
You have to factor in resolution and contrast. I've not idea what the resp. resolutions are, I'm just pointing out that a 1.4" at, say, 640x480, can display exactly the same amount of information as 2.5" screen at 640x480. The only issue is whether the the smaller screen is sufficiently crisp to make the smaller glyphs visible -- all Teric reviews I've seen say it is.
(That said, for my diving I'd take an e-ink screen and 2 years battery life over either of the above any day.)