Yes, the Trident Align ball marker has been deemed legal under the rules of golf by golfs governing bodies. Due to the markers small size it is not considered to be an alignment aid and is permitted under section "Equipment and Other Devices", rule 6.7.

The alignment finder can aim 20 degrees left and 20 degrees right from its central position. The distance this equates to the left or right of the hole in feet or inches varies depending on the overall length of the putt.

The Trident Alignment Finder can cope with any amount of break. If a putt has a significant amount of break then generally you can see this as you approach the green to mark your golf ball. In this case, you position the Trident Alignment Finder on the ground aimed more towards the side that the putt will break from. Rather than starting with the alignment finder in its centered position with the long centre line aimed directly at the hole, you place it on the ground aiming further to the left or right of the hole and then adjust accordingly.

It’s 1.38″ wide, 1.50″ long and a depth of 0.22″.

The Full Metal marker is only 34g and the 2.0 marker is only 26g, both light enough that you don't even feel them in your pocket!

There may be an occasion where your Trident Align ball marker is close to your playing partner’s line of putt. Out of courtesy, you can simply use the 25mm marker coin instead, this does not impede their line or catch their eye. Once your playing partner has played you can put your Trident Align marker back down and continue as normal. 

You can use any colour marker pen that you prefer to make the Trident stencil on your golf ball, however, the black marker pen produces the best contrast and visibility between the markings on the golf ball and Trident Alignment guide unless you purchase a green, red or blue Full Metal separately to match up with your preferred marker colour.