The problem with betta is you will pretty much always get differing opinions, I kept and bred thousands of betta, male betta should always be kept alone, betta do not do well in pairs, groups etc the area where this differs is with females, females can be kept together but I always advise groups of 6+ as a minimum, even all females groups will show aggression to each other, one of the most understood thing about betta is that they are not like most fish each and every betta have there own personality some are extremely placid where others can act and only be described as evil, betta in community tanks are hit and miss ( same in shrimp tanks) some will terroris everything in the tank others will be tore to pieces, most tetras and barbs etc will harass betta none stop normally resulting in disease and or death of the betta ( normally ) in short I guess what im saying betta should be kept alone and if tank mates are desired then things like corys, ottos etc are the only real options imo
Mark