A person must use telegram, must trust you and must have some btc for play with this. I don't think that works, sorry.
Telegram is multi-platform. Has Android, iOS, Windows, MacOS, Linux and a web client... hell it even has WindowsPhone which is usually ignored by everybody! To be honest, this comment is almost the same as saying "You must use a web browser" as a reason not to use a service.
I do agree that there is an implied level of trust here. That they will not run off with your money and will pay out. But this is also true of pretty much all online casino/sportsbooks. Just because it doesn't have the $$$ to spend on fancy websites, doesn't mean it is a scam. Hell, look at HashOcean... that had a plenty fancy website... that disappeared overnight with millions of dollars worth of bitcoins!
How to get around this? Play small... Only deposit when you wish to make a bet... don't hold large amounts of bitcoins in the service for extended periods of time... you know, all the common sense stuff you do with any 3rd party service that you are trusting with your precious BTC
Must have some BTC is also a relatively valid, but I'd say minor, concern. I guess for a lot of people, not being able to put funds in from fiat services like credit cards, Paypal etc would be problematic. But there are plenty of other services online that allow you to buy bitcoins using fiat, which you could use to purchase your bitcoins and transfer them over... so I don't see it as being a HUGE issue...