The Sekonic 558 is not heavy...but IMO it is poor ergonomically, overkill with features, weakly built, and the digital readout is a less-than-ideal (less-than-intelligent?) design for those who use reflected meters for tonal placement. It is thoroughly representative of modern all-in-one whiz-bang electronics for the masses: jack of all trades, but master of none...and heaven forbid you should have to repair it. The all-in-one nature of it is a big draw, though. I would already own one if it wasn't for the poor build, lack of an analog dial, and overly complex and uncomfortable controls. If you really don't like the 558 for any of these reasons, get a Pentax Digital Spotmeter and you will be fine. It is the K-1000 of light meters. Simple, simple, simple, and durable, durable, durable. Mine is on its third life after a few events that would have killed a 558 for good. Basic, to the point, tough, and made for people who already know what they are doing; who need/want something that simply reads light, and leaves the rest to the user. It's the ideal reflected meter for field work, assuming you understand reflected metering techniques. It is the antithesis of the aforementioned whiz-bang gizmos. It is a sensibly designed specialty tool built to last, built to be serviceable, and designed to be used by someone who is already technically competent. All I want is one button that gives me an EV, and a scale to look at.
Take your pick. Both are good tools, but for different reasons. If these things that I dislike about the 558 are not a problem for you, and the only reasons you don't like the 558 are the size and weight, I would just deal with it. Get bigger pockets.
They are not large and not heavy for what they are, and are not expensive considering that they take the place of three meters. Great idea, poor execution, IMO. Great studio meter, but I would be afraid of farting near it for fear it would break, so would never take it anywhere in my pocket or treat it the way I treat my "out and about" cameras. The way the equivalent exposures are displayed and cycled makes no sense to me for reflected use for tonal placement.
The Pentaxes are expensive, but are well built and easy/clear to operate, plus they are a current item that you can get brand new, so will be supportable for quite some time into the future. The only place I know that still actually sells them is Calumet. They are $500 plus tax. If you find a new one for less, it is an Internet scam for sure. I walked in and bought mine after finally giving up on rigging batteries for my Pentax 1/21.
If you can get a used one that is Zone VI modified for under $350, perhaps $400 for an extra clean one, I would say that is a better buy than getting a new one for $500. The modifications never made that much of a difference when I used my instructor's for a few months, but better to have them than not.
2F/2F
