I use an Ian Golds with a conversion kit to make it into a double header. I find it good on sand/shingle beaches, only problem I have with it is height, I rather the height of the tripods to lift the rod tips because of wind or weed. This is mostly outweighed by the convenience of transporting the spike.
I have a couple of ones sold by Veals Mail Order.
The ones I have are double headed sand spikes.
They also sell single-rod ones.
I can't compare them with other makes as I haven't used any others since time immemorial.
The only fault I could find with mine are that they don't have a "foot peg" on the side of the shaft to help with pushing the spike into very firm ground - so you end up pushing or stepping on the top end of the rest (and if you slipped could put a lot of weight on one side of the double head....twisting it; haven't done that yet)
Do you know anywhere to buy some Alloy angle strips. If you do with the use of some cheap Plastic cups for holding the rod butt in and and other alloy metal for the rod holder top..if you use some plumming foam for the arms. you could make it yourself for very little, and you could make different ones for the different ground you fish off.