I'd think that the issues you'd encounter with a Japanese bowl (porosity, thermal transference) would be similar in a western-style raku vessel... assuming, of course, that there was nothing toxic in the glaze.
One of the key "values" of actual Raku ware to a chajin (tea person) is that aspect of the insulating thermal transference quailties you mention. Another is the very light weight. And yet anotehr is the clear fragility of the work (wabi-sabi coming into play). Another highly valued quality in Raku is not somehting that most people not really familiar with Chado are aware of; the sound the whisk makes in Raku wares. Sound is a key component of tea ceremony (every sense is important). Vitrified wares tend to make a harsher sound when the tea is whisked.
Japan is a different place. They have a different legal system. They value ceramics differently. They value "tradition" (in some cases ) diffetently. True Japanese Raku ware is lead glazed. To this day. Laws in Japan tend make exceptions for "artisanal wares".....because they are important. So technically the glazes on those pieces have some real "potential issues" by modern standards.
BUT......... a Japanese Raku teabowl will be put to one use and one use only. It will be used to serve matcha. No one is going to "defile" it by doing anything else. Raku chawan are "revered" objects. Almost like a religious icon (but Chanoyu is NOT a religous ceremony, although Zen values permeate it). And the real ones (Raku family and/or Ohi family) typically are absurdly expensive, although you certainly can find more mass produced ones that are much lower priced.
One of the first things that is done in a real Chakai (tea ceremony gathering) is that the host cleans everything in sight before the guests arrive.... including the utensils. So any film of white lead oxide that forms on the surface of the raw lead glaze is well washed away then. During the cremony itself (shortly after the "big cleaning") the host again ritually cleans the bowl before use. SO by the time tea is made in the bowl, it is well cleaned of potential lead residues that will form on the surface.
The amount of time that the tea in the bowls is, as I mentioned, literally only minutes. For a serving, there is only a small amount of tea in the very bottom of the form. For usucha (thin tea) it is meant to be drunk in about 3 sips. For koicha (thick tea) there is more and it is shared by multiple people, but still very little material in the bottom of the bowl. Leaching tinme and surface exposure is minimal.
I have Raku bowls. In a setting with my students, they are used for display and handling only. In a "tea" setting with "consenting adults", I use them.
The reason I asked about the red is that it looks like a cadmium based red. Hopefully they are using an encapsulated form. Even still........ if you haven't looked at the FDA laws on lead and cadmium use with food wares.... you likely should. Just so you are familiar with them in your decision making process.
I looked at the Duncan Envision MSDS that I could find. I wasn't impressed with its thoroughness. First of all....... there are no individual ones that I could easily find for the individual colors. So the "generic one' seems to me to be night on to useless to guage the actual content.
I've related this story before about a "food safe" non-toxic labeled product from one major manufacturer that I was wanting to use. I called to talk to their tech support folks to get an answer about any lead being in the product, since I make food wares and the FDA laws require that I know about that potential fact.. I got told by the people I first got sent to ... nope... none in there. But from talking to them and asking questions, I became well aware that I knew well more about technical ceramics than they did. These were their "tech support staff" that 99% of potters calling them would get. I kept asking for someone further up the technical "food chain". After a few layers and people who clearly could not answer a real techniocal enquiry, I finally asked them if they had a ceramic engineer type person on their staff. They said they did. I asked to talk to him. In about 1 minute or less I had my answer. Yup... lead in there. Those products are still sold by that company as "food safe".
The whole "non-toxic rating" can be a bit of a "game" on MDSDs and product labeling. You'll notice that the boxes of clay you get often have the ASTM non-toxic ratings on them. And they are. As THAT product..... which is what is being rated. It is really hard to inhale a wet mass of plastic clay. Ah,.... but let that clay dry out ..............and there you have respirable micro-crystaline silica in that stuff. A known human carcinogen, a causer of silicosis, and an OSHA regulated compound in the workplace. They can be sold as non-toxic... because they are wet . Ditto for glazes.
Unfortunately, there is a lot to this stuff.