Gels can cause issues, its a breeding ground for bacteria, maybe the new gels don't.
Why do you want to use gel when you can use water which is the best in my opinion and i guarantee 99% if not 100% of the best tarantula guys on this forum use plain old God given aqua!!
1) Water gel costs money not much but if you have +100 spiders its not viable.
2) Water gel gets dirty fast, 80% of the time your spider will deposit its poo and eaten food into the water bowl, therefor it needs to be cleaned on a regular basis water gel again will cost you money, water is almost free.
To put it plain keep it simple with you spiders, water is natural, water is made for animals, water is best

It may seem cool and fancy to use water gel and you may think your spider likes it..... i beg to differ..
Hope this helps.