Liquitex is a company founded in 1955 that makes paints and inks. This is also the company that invented the first water-based acrylic paint. Fast forward today, this is quite a well known company that sells a huge variety of liquid ink and paint products.
The Liquitex Acrylic Marker is a pigmented acrylic paint marker that's available with 50 colours, including six fluorescent colours. You can download this PDF to look at all the colours.
The markers are available individually and in sets. Price range for each marker is from US $5 to $9. You can compare the prices on BLICK Art Materials which has the full range, and on Amazon which has a smaller range.
Tips available are 2mm and 15mm chisel tips, and these are replaceable.
The markers can be dismantled easily for refilling. However, Liquitex doesn't actually sell refillable acrylic inks for these markers. I'm not sure if you can use the bottled Liquitex Acrylic Inks (Amazon | Blick). If the bottled inks dry too fast, then they won't be suitable for use in markers as the tips will dry out quickly and get damaged.
One refillable ink option is to get Molotov acrylic ink refills which has better opacity.
The pigments used to create the colours are listed. You can check the pigments to determine the lightfast quality. Most of the pigments are lightfast.
Since the inks are pigmented, you can use fixative over the inks and the colours will not break apart.
And the inks don't smell
The tips are spring loaded. You push the tips in to get more ink out.
Ink flow is good. The strokes are wet and colours look vibrant on white paper.
The ink dries quite quickly on paper to a matte surface. The company says the ink dries to a satin finish.
The ink can work on paper, canvas, wood, plastic and fabric. Ink is waterproof and permanent when dry.
The thin and broad sides of the tip can create 2mm and 4mm thick lines.
The ink is supposed to be opaque but it's not completely opaque.
The second and third horizontal strokes were painted with 2 and 3 layers.
Against black or dark coloured paper surface, you can see the ink is not completely opaque and needs several layers to improve opacity.
Multiple layers is definitely needed if you want more opacity.
Overall opacity is actually not bad with slight colour pass through from the first layer of colour underneath. These markers probably work better on lighter coloured paper surfaces.