I can only comment on the 1953 era Rockets, since I have one. There are sample-to-sample variations, meaning you could get a good one, or one not so good.

The carriage return lever is very short. You'd be just as happy pushing the carriage back via the right platen knob and then indexing the line manually. And the typing feel is not like the bigger Hermes. There is no touch adjustment, ribbon color selector or tabs. So don't use a red/black ribbon. Instead, use all black and when one edge wears out, flip the ribbon over to use the other side. It truly is one of the smallest typewriters, so compromises were made. But I love mine, and it works good, making a dark imprint. It's small enough to fit in a shoulder bag.

I wouldn't want a Rocket to be my only typewriter, but they're great portables for typing on the go.

~Joe

I have a '64 Rocket (see below) and unlike those mentioned in the previous two posts, it does have a colour selector and the line space lever is very large. It may not have a touch control system, but then again I don't think it needs one as the type action is fairly light. It's also true that it doesn't type like a larger portable, just as a larger portable doesn't type like a standard; however, whatever the perceived compromises might be with this ultra-portable they aren't substantial enough to overshadow the added portability this model has over a full-sized portable. If I was travelling I would be more than content to use a Rocket for regular typing duties, but it certainly wouldn't be my first choice in the size category.

 

Lettera 22. But the Olivettis aren't THAT small.

I have a 1961 Baby and it does have a really nice typing feel actually. It's the crossover model where it still has the gullwing ribbon covers and it also has a colour selector. Mine has something weird going on where the shift doesn't work sometimes when it's in the body - take it out to have a look and it works fine. Put it back in and it either doesn't, or else does for a bit and then at some point doesn't. It's an ee cummings typewriter.

I've had a few Splendids and SFs go funny on me, and I've never met a Skyriter that seemed in any way robust or typed a nice page - though they do FEEL nice to use. I have one right now that I hate to even charge money for because even with a fresh black ribbon in it it produces insanely pale print... I think the issue is that the ultra-portables got so much more heavily used than everything else. 

I have a Groma Kolibri that feels great and types beautifully, and I love it. But it weighs a LOT for a flat machine. And it's not a SPEED typer. My midsize (but very compact) Halda might even weigh less than the Kolibri. 

Ultimately I think of the flats, the Olivettis behave more like a midsize: more solid, more reliable.