Grey Card vs White Filter vs Spyder

Since I've been taking more and more shots with old manual-focus lenses these days, even with the 7D (which allegedly has great Auto White Balance), I've noticed the colours are a bit out.
It's most visible with an Asahi Pentax Takumar 50/1.4 I got recently. I love it already, built like a zeiss tank and sharper than the nifty fifty by a long shot. Problem is, it has the same problem a lot of Takumars get, some elements in the glass react with age and the whole thing goes yellow. I've tried the trick of putting it in the sun, the UV has gotten rid of some of the yellowness, but there's still some there.
Have some sample photos why not, Takumar vs NiftyFifty at f/4, Camera's Auto White Balance, dpp-raw converted.
Attachment 285Attachment 286
Thankfully for this shot, there were a few signs around the place whence to get a 'click' white balance.

But in general, I've been wanting to add one to my kit anyway, question is, what to get?
I know some of you use the Spyder Cube, but they're fairly steep at $75 around here.
I've found some genuine Kodak Grey Cards for about half that online, and cheaper-brands are a lot less again. Also a lot easier to slip into the laptop-slot in my bag that a spydercube taking up a lens-space (how big are they?)
But then there's the "white balance filter" style, which i'm presuming you just put over your lens, take a shot, then use that for custom white balance for future shots. They go down to practically free on ebay (there may be a bit of a "you get what you pay for" situation) up to $100 for an expodisc.

So who's used what types of system, brand-name or rip-off, what's your experiences and what would you recommend?

Hi, I would say this depends on your requirements. If exact/true color matching is important I suppose you need more accurate tools than grey cards. The only accessory I have for this is a no-name grey card that I use now and then. I normally shoot AWB without any grey card involved and, if necessary, I tweak WB in post to something I like. This “method” is highly subjective but usually gives satisfactory results. In some situations the AWB has difficulties and then I set manual WB in camera either using the grey card or some neutral object on site (e.g. ice on concrete). This method usually gives a good starting point for further tweaking in post. (“True” white balance isn’t necessary the setting that gives the best result - this is, again, highly subjective.)

So, basically, my recommendation for general purpose photography would be to get a grey card. My no-name card works fine for me, but possibly the more expensive branded cards are better - I don't know. Grey cards are quite useful, not too expensive, convenient to transport/use and do a good job getting an estimation of the “true” white balance. (If you really want to get control of exact color matching you would need something more.)

What about a colored filter to offset the amber cast that could always be left on the lens? Having to go to a custom white balance everytime you change lenses would get old, but yes, it can be done along with the color shift screen option.

I use Michael Tapes WhiBal reference card. Size and density of a credit card and I literally carry it in my wallet. Whenever the light cast is iffy I simply shoot one frame of the reference card under that light. In post I use it to set the white balance and then apply that color temperature to all the other shots taken in the same light. If my exposure is iffy, I use the black and white points to set my base histogram. Frankly though, I often like the resulting color cast and don't bother with the adjustments.

Hi Dr C. I use a grey card. I either shot a reference frame like Don or I shoot the grey card itself (if I have the time) and set my custom WB to that frame. I am very happy with the grey card. I bought it for 4 or $5 at an old camera repair shop. Its cardboard, 8 x 11. I cut it up to 4 x 6 and it has a nice home in my camera bag. Good luck with your decision.

Damian