I have to say that looking at the specs and prices the LAP-C looks pretty darn good and it has a CAN decoder. But if you don't need the speed then there's little benefit.
As for the 512k buffer, do the maths re sample rates for your typical app (CAN @ 1MHz?). At 10x1MHz sample that's only .5 seconds of sample which isn't great. OTOH if it is clever and only samples deltas then it might be OK.
With the Saleae you can sample for a forthnight then drill down to the important bit, same with the USBee it looks like and that also has a CAN decoder.
Note: I've only looked at the Saleae, USBee and Zeroplus
so I can't comment on the others. I have a USBee SX and have extensively played with the demo software for the other 2.
As far as "sampling for a forthnight" it depends on your environment.
Also, better triggering capability, can often eliminate the need for having to sample so much data.
A big difference is that the ZeroPlus design has full buffer memory inside the device. The Saleae and the USBee do not.
What that means is that the Saleae and the USBee need a very fast USB bus with no other devices sharing it (to avoid any lantency) in order to function because their internal memory is very limited.
The LogicCube "takes a picture" of the lines and stores all the samples inside the memory first and then dumps that full trace across the USB.
The other two stream the data to the host in real time using only a very small buffer inside the device.
Also, the best I can tell, is that the LogicCube has trigger logic inside the device and the other two (at least the USBee) stream all
the data to the host and then handle the triggering in the host by looking at the incoming data in real-time.
It works but requires a very fast low latency USB.
The logicCube also has some methods of compressing the data samples so that you don't need to store the full data on each sample. This can extend the buffer to act as a larger buffer.
I have a USBee SX and it is nice but when using Vista (dual core 2.8ghz Athlon on an HP slimline) it had problems keeping the USB bus streaming so traces would fail at the higher sample rates > ~12mhz. (worked fine with XP on my Acer Netbook at full 24Mhz sample rate)
The Saleae is a similar design to the Saleae but also has support for MAC and Linux so you are not stuck having to use Windows.
Since the Zero Plus has its full trace memory internal to the device the USB speed and its latencies are removed. This means that you could run the ZeroPlus and its software in environments like a VM or on slower processors or loaded USB busses than would not be possible with the Saleae or USBee.
The ZeroPlus design will allow it to always operate at its maximum sample rate of 100mz where as the other designs
will require you to lower your sample rate to deal with USB latencies
and in some cases it may not work at all, like under a VM.
Remember that with USB even devices that are "idle" consume USB bandwidth (thank you Intel) and if they are slow speed devices like perhaps a keyboard or mouse, your bandwidth is dramatically affected if those slow devices are sharing the same USB internally.
A single slow device on a USB will halve the USB bandwidth available to a highspeed device if they are on the same USB even if the slow speed device is "doing nothing" - that is a limitation of the USB protocol.
With respect to pricing of the ZeroPlus, pay close attention to what comes "in the box". Often the low end 032 model does not come with all the clips. That can add $20-30. Yet the 064 model often does come with the clips so it isn't as much more as it might look at first to jump from the 032 to the 064 model.
The USBee can act as a signal generator as well as analyzer. You can define waves or even play back sequences on multiple pins. This can be a very useful feature to simulate hardware.
USBee has more signals than the Saleae.
The USBee can be clocked with an external clock and has a separate trigger so you can sample 8 full data lines using an external trigger. You cannot do this on the Saleae.
(Obviously you can also do this on the Zeroplus as it has 16 lines)
To me it comes down to a few features that will make the decision.
If you need more than 8 signals - ZeroPlus wins.
If you need native MAC or Linux support Saleae wins.
If you want signal generator support USBee wins.
If you need higher than 24mhz sampling rate or want to avoid USB latency issues ZeroPlus wins.
(Remember that you need the sample rate to be at least double your signal rate so 24mhz means you are limited to about 12 mhz signals)
If you need an external trigger with more than 7 data lines, avoid Saleae.
If you want/need HUGEly long traces, avoid the LogicCube.
(But keep in mind that if you slow the LogicCube down to 24Mz the trace will be quite large)
They all have their pluses and minuses.
At the time I made my decision (about a year ago) the USBee s/w was better and I opted for it. However, in my case I often find myself needing more than 8 signal lines and higher sample rates and so the LogicCube would have been a better choice for me.
(I often use my analyzer to time software or look at hardware strobes and a 24Mhz sampling rate isn't good enough as you can only reliably measure down to about 80ns with it)